We've focused on Android but most of our tips also apply to iOS and Windows Phone.
Please add your own questions in the comments below and we'll do our best to answer them. Tips, tricks and alternative solutions are also welcome.
Why is my phone hot? How to fix a hot phone
In the days of increasingly slim phones and metal- rather than plastic cases, a phone that gets warm in use is not at all uncommon. All consumer tech can get hot in use, although there are three key things that will make your phone get hot: when it is being taxed with intensive tasks, while it is charging, and often when you have a poor signal.
While some heat is normal, excessive heat isn't good for your smartphone's battery. You could try removing the case (or removing it from your pocket) to allow it to cool down a little, reduce the number of things you're trying to do on it at once, and unplug it once it's finished charging. If it's really hot, you could also turn it off for a short while to give it a rest.
Working out exactly where on the phone the heat is coming from can also help you work out how to tackle the problem - it could be the screen, the battery or the processor, for example. If you've recently installed a software update, this could also be causing problems. Also see: Best new phones coming in 2015/2016.
Why is my phone so slow? How to fix a slow phone
If your phone was once fast and is now slow, but otherwise seems to be functioning properly, the most common cause is a build-up of apps, data, temporary files and other junk. It's also possible a particular app or software update is causing problems, although less likely. Even less likely is that malware is slowing down your Android phone, although if you think that may be to blame also see our advice on removing a virus from Android.
Go through your phone and remove anything you don't need or use. Apps you don't use can be uninstalled (including those that may have been preinstalled when you bought the phone - if you are able to do so); photos, video and other media can be backed up and then removed (see how to back up Android); your Downloads folder can be emptied; and you can also clear your data cache. For the latter, head to Settings, Storage, tap on Cached data and then select Delete. You can also delete cached data for individual apps from Settings, Apps.
Doing all this should speed up your phone, but it can take time. An easier option can be a factory resest, which will return your phone to its out-of-box condition, but beware that you will lose anything that is not backed up. We're not just talking about photos and video here, since you will also lose your downloaded apps and any in-game progress not linked to the Play store. Rest assured that you will be able to re-download any apps previously bought from Google Play without paying again.
If you're sure you want to perform a factory reset, go to Settings, Backup and reset, Factory data reset. This process will remove everything from your device except Android itself.
Files stored on a removable memory card will not be touched by a factory reset, but if your phone is still slow it could be the microSD card causing problems. First try removing it from the phone and see if performance is affected. If the microSD card seems to be causing problems, attach your phone to a PC and back up the memory card's contents by copying everything over to the PC. Go to Settings, Storage and opt to format the card, then plug it back into the PC and copy back only the files you really need. If you later find some apps don't work properly it's likely because some of their files were installed on the memory card; just uninstall and reinstall them to get them working.
Other things you can do to speed up your Android phone are to disable animations and extras, close multiple running apps, and if you have several try removing some widgets from your home screen. Sometimes the simplest fix is to restart your phone (some people can go months without doing so). Also see: What's the fastest phone 2015?
Why is my phone full? How to increase phone storage
Phone storage is quickly filled with apps, data, photos, video, music and more. If your phone has only 4-, 8- or even 16GB of internal storage, it's very likely that you will run out of space, at which point you may receive an 'insufficient storage available' error message when trying to download a new app (also see: How to fix Android's "insufficient storage available error). Even if you don't think that you have too much stuff installed on your phone, remember that the Android OS alone consumes a couple of gigs.
You can try the tips outlined above in 'Why is my phone so slow?' to claw back some storage space, or you can use some additional methods to gain more space.
The easiest way to add storage is with a microSD card, if your phone supports one. Note, though, that not all apps can be saved to microSD. Other solutions include utilising cloud storage, hooking up USB OTG storage and connecting to a wireless hard drive. Also see: How to add storage to Android.
Why is my phone in Safe mode? How to get out of Safe mode
Safe mode is a useful feature when you're troubleshooting a problematic Android phone, but it's also easy to accidentally put your phone into Safe mode and then get stuck there.
It's easy to accidentally enter Safe mode (you'll know you're in Safe mode because it will be written at the bottom corner of the screen). On my Samsung Galaxy S6, for example, if I turn on the phone while holding down the volume-down button (easily done if it's in your hand) then it will automatically enter Safe mode. On other phones, you might enter Safe mode by pressing and holding the power off option in the power button menu for a few seconds, then simply accepting the prompt that pops up without paying attention to what it is asking you.
Getting out of Safe mode is usually as simple as restarting the phone. If you find the phone is still restarting in Safe mode it's likely that your volume button is sticking or there is another hardware issue at fault.
Why is my phone in Recovery mode? How to exit Recovery mode
Recovery mode is not the same thing as Safe mode, outlined above, but it is also used for Android troubleshooting and, well, recovery. Recovery mode is more remininscent of a PC's BIOS, and can be used to bypass the normal loading procedure in order to factory reset the phone, install updates from an SD card or a custom ROM, for example.
As with Safe mode, if you find yourself in Recovery mode without intending to access it then it's probable you did so accidentally, usually by holding down the power and volume-down buttons while the phone is booting.
Within Recovery mode you can use the volume-up- and -down buttons to cycle through menus, and the power button to select options. Be very careful what you press here - if all you want to do is exit Recovery mode look for an option to 'Reboot system now'. To learn more about Recovery mode see Use Recovery mode for troubleshooting Android phones.
Why is my phone saying no SIM? Why is my phone saying no service? Why is my phone saying emergency calls only?
If your phone is reporting that no SIM is installed then the most likely explanation is that your SIM is either not installed or incorrectly inserted. Try taking the SIM out the phone, ensuring that it's clean (and that the space inside the phone is also clean), and reinserting it correctly. If it sits in a SIM tray, ensure the tray is the correct way up and fully pushed in. (Incidentally, if you're having trouble removing your SIM tray, push harder on the release pin.) Also try restarting your phone and checking that all software updates have been applied.
If it is a brand-new SIM then it's possible it hasn't been activated. Contact your mobile operator for help.
If you're absolutely certain that your SIM is activated and correctly inserted and the phone is still reporting no SIM or SIM missing then it's most likely a problem with either the hardware or the SIM itself (if it's damaged then request a replacement from your mobile operator), or your service has been cancelled (again, contact your mobile operator). The best way to check for sure whether it is your phone or the SIM at fault is to borrow a friend's SIM and check whether it is recognised by the device.
If you have no service you either have no reception (in which case it will allow you to make emergency calls only) or there is an issue with your SIM card.
If you have no reception on your phone also check you haven't got it in Flight mode - look for an aeroplane icon in the notification bar. Also see: Best phones 2015.
Why is my phone bill so high? Why is my phone eating so much data? How to reduce phone bill
This may not be the answer you want, but if your mobile phone bill is high then it's because you've been overspending, possibly without realising. With most mobile contracts now offering free minutes and texts, it's usually data that is to blame. However, it's worth checking your phone bill to see how many minutes and texts you use on an average month and upgrading your package if necessary.
Data is what's usually behind huge phone bills. Even when you think you're not using it certain apps will be running services in the background, periodically checking for new emails or weather updates and the like. One fix for this is to connect to a Wi-Fi network whenever possible and keep tabs on your mobile data usage. You can set an alert for when you're nearing your data allowance, then opt to turn off mobile data until the month is over. Read our tips on how to minimise data usage.
As with minutes and texts, check your bill to see how much data you're using. If necessary, upgrade your contract or add a data bolt-on. An extra fiver a month might not sound good now, but it will prove a lot cheaper when your operator begins charging you £6.50 for every 250MB you go over your limit.
Services such as WhatsApp use a tiny amount of data, but streaming video and downloading large apps can quickly eat through your allowance. We can't tell you exactly how much data you need without knowing your personal circumstances, but personally I have never been able to stick to anything under 2GB. Now that I have a 4G contract it's easy to eat through data much quicker than I realise, and I have therefore upgraded to a 6GB contract. That seems to be sufficient for me personally.
Roaming is another cause for huge phone bills. When you go abroad you are charged more for the calls, minutes and data you use, even if they are free on your contract back home. A solution to this is to turn off data roaming (Settings, Mobile Networks, Data Roaming), but if you still want to be able to use your phone abroad then you need to work out how to do so as cheaply as possible before you leave home.
All mobile operators have plans that let you use your UK minutes, texts and data abroad for a fixed price per day. Three has also introduced its Feel At Home programme, whereby it doesn't charge you for roaming in several European countries. Read more about roaming in our article How to avoid data roaming charges.
If you haven't been using your phone abroad, and are certain you aren't overspending on data, text or minutes, check an itemised bill to see exactly what you're being charged for. If you're having problems managing your phone bill, speak to your mobile operator who will be able to advise you on what to do next and also, if necessary, set an expenditure limit on your account.
Why is my phone roaming?
If your phone is 'roaming' then it means you are accessing a different network to your home network. Be aware that when using your phone abroad you will be charged extra for the minutes, texts and data you use unless you are subscribed to a special roaming package (see above). You can turn off data roaming in Settings, Mobile Networks, Data Roaming.
Note that even when you turn off data roaming you will still be charged for any calls and texts you make, but not those that you receive.
Why is my phone battery so bad? How to fix poor battery life
All batteries degrade over time, but even new phones can struggle to make it through a full working day thanks to increased usage, larger, higher-resolution screens, more powerful hardware and so forth. Rather than going out of your way to change the way you use your smartphone to improve battery life, our favourite 'fix' is to carry a portable power bank - then you'll never run out of juice. See our round-up of the best power banks.
The truth is it is incredibly difficult to 'fix' poor battery life, because it's very rarely one definable thing that is causing the problem.
If your phone's battery is removable, a 'fix' may be to buy and fit a replacement battery. Most flagship phones these days do not allow the user to access the battery, however, and if it's a software issue then fitting a new battery won't help.
Software updates that haven't been optimised for your phone's older hardware are a common problem, but other than waiting for the manufacturer to roll out a new update there's little you can do.
There are plenty of recommended tips you can try that may or may not improve your situation. Restart your phone every once in a while. Take steps to avoid your phone becoming too hot (see above) or too cold. Turn down screen brightness and adjust the screen timeout setting. Turn off Bluetooth and Wi-Fi when you're not using them. Close multiple apps running in the background. Turn off haptic (vibration) feedback. Turn off live wallpaper and animations. Reduce the phone's volume when playing media. Take advantage of power saving modes. Unplug your phone once it's finished charging. That's just a few - for more advice on improving smartphone battery life see How to make your phone's battery last longer.
Why is my phone charging slowly? How to charge your phone faster
When you need to charge your phone quickly before you leave home, the last thing you need is to find your phone is charging slowly.
In order to 'fix' this issue we need to look at the hardware you're using to charge your phone. If a phone has for no apparent reason suddenly started to charge slowly then it could be an issue with the USB cable, the charger, or even the phone's battery or charging connection itself. Also see: How to charge your phone or tablet faster.
First, the USB cable. It's often recommended that you use the USB cable supplied with the phone for charging. You absolutely don't need to do that, but it's a way of avoiding you using some cheap, inferior cable in its place. You should also check your cable for damage, and that the connector itself still fits snugly in the phone. If in doubt, get a new cable. Also check that the connection on your phone is free from dust and grime.
Second, the charger. These days it's becoming increasingly rare that a mains adaptor is supplied with your smartphone. This makes sense, given that you don't need multiple identical chargers for every piece of consumer tech you own. However, it also means you could be using an old USB adaptor that is underpowered for your device.
Worse still is when USB chargers are supplied with your phone, but they don't offer the fastest way to charge that phone. (We'd rather not have one supplied.)
When we talk about charging phones we tend to talk about standard-, fast- and quick chargers. Standard phone chargers are typically rated at 5W, but most modern smartphones will accept a higher wattage, such as that offered by the chargers typically sold with tablets. What we call 'fast' chargers may offer between 10- and 12.5W, which means you could potentially charge your phone in half the time.
Quick Charging is a Qualcomm technology supported by many flagship phones running certain Snapdragon processors. Quick Charge 1.0 can reduce charging time by up to 40 percent over standard chargers, Quick Charge 2.0 by up to 75 percent, and the newly announced Quick Charge 3.0 by up to 80 percent. In order to benefit you must use a compatible charger, however.
If you're not sure how much power your phone will accept, don't worry. It will draw only the power it requires.
Wireless chargers (typically 5W) and a PC or laptop's USB ports (2.5W USB 1.0 and USB 2.0, 4.5W USB 3.0) will charge a phone much slower than can a USB mains adaptor, so if you're in a rush don't use one of these.
Other tips thrown around for improving phone charging are to remove the case (thereby avoiding heat build-up), and to turn it off or put it into Flight mode. Try not to use it while it's charging either.
As in our previous answer, our preferred solution is not to worry about how long your phone takes to charge before you leave home, but to carry a power bank so you can recharge it wherever you are.
Why is my phone data so slow? Why is my phone internet not working? How to fix your mobile internet connection
Firstly, it's important to note the differences between mobile connectivity standards, as we've explained in our guide to mobile connectivity.
4G is the fastest mobile data connection, with Wi-Fi like speeds for accessing the mobile web. Indeed, it's the next best thing to connecting to Wi-Fi for getting online from your phone. However, not all of the UK is covered by 4G networks, and not all phone contracts include it - check with your mobile operator whether you would be able to benefit from 4G.
3G is also usefully fast for browsing the internet from a smartphone, but anything other than this (such as GPRS and Edge) are too slow to even think about using to get online.
If you are connected to either 4G, 3G or Wi-Fi on your phone and your internet is slow, it may be a problem with your connection or signal strength.
If your internet is slow you should ensure you don't have other internet tasks running in the background slowing down your connection, such as app downloads (you can set these to download over Wi-Fi only within Google Play).
Sometimes we find closing and restarting the browser can make a huge difference if it gets stuck trying to load a page.
You can also increase the amount of memory available to Google Chrome. In your smartphone browser head to chrome://flags/#max-tiles-for-interest-area and change the drop-down from default (128MB) to 512MB. Tap Relaunch Chrome to save the changes.
Occasionally it can be congestion or a problem with the mobile network causing internet problems, too. A good idea is to check Twitter to see whether others are experiencing the same problems.
If your internet is not working at all, check that you don't have the phone in Flight mode (look for an aeroplane icon in the notification bar).
For more tips see how to speed up Android browsing.
Why is my phone speaker so quiet? How to increase in-call volume
Pressing the physical volume buttons on an Android phone let you alter the volume for phone calls and notifications, alarms, media and system sounds; these controls are also available within the Settings menu.
If you find your phone too quiet when you're talking on the phone then it's actually the in-call volume you need to increase. This is easily achievable using the volume keys, but only while a phone call is active. Once you reach the maximum in-call volume you will hear a beep.
If your phone's speaker is too quiet when playing music without earphones, check that it isn't being muffled - if the speaker is at the rear you may need to remove your phone case, hold it differently so audio isn't directed into your palm, or place it face down. You should also check you have the media volume turned up, accessible from the Settings menu or by pressing the physical volume buttons while music is playing, a video is streaming or a game is being played.
Why is my phone not ringing? Why is my phone not sending/receiving texts?
If you can't hear your phone ringing, it may be that you have inadvertently put it on Silent mode. Check this in Settings, Sounds and notifications, Sound mode. Also within the Sounds and Notifications menu check the Volume setting, since it may be set so low that you can't hear it.
If phone calls are not getting through to your phone then you either have it in Flight mode or you have no reception. Or you've been cut off - have you paid your bill?
This may also be the issue if your phone is not sending or receiving texts, or it may be that your message server settings are incorrect. Check your mobile operators support pages or ask them for help in how to correctly configure your message server settings.
Why is my phone rooted?
A rooted phone really isn't as scary as it sounds, and it can be treated exactly like an unrooted phone if you have no desire to take advantage of its root control.
Rooting an Android device is the process of gaining privileged or full control of the operating system. It's a bit like having a VIP pass at a gig, which allows you to go anywhere you like and do anything you want (within reason). Rooting an Android smartphone or tablet is effectively the same as 'jailbreaking' an iPhone.
Whereas most smartphones sold in the UK are sold unrooted, elsewhere in the world - particularly China in our experience - they are more frequently sold rooted. Learn more about rooting Android in our beginner's guide to rooting.
Read next: Best Android phones 2015.
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