I use PAYG on T-mobile on my phone and I pay £20 for six months access to the internet. It has been useful coupling my laptop to the phone to gain access to the Internet when, say on holiday. There is probably a limit to the amount that I can download but for occasional internet usage it is OK.
What you can do will also depend on the type of phone and your provider. Many "smart phones" will connect with HSDPA or 3G and then act as a WiFi Hotspot for access by a Laptop, Netbook etc. The phone is effectively a wireless router.
The "O2" and "3" networks allow this without extra charge, Orange and T-Mobile charge extra, with Orange only allowing iPhone users to do it. Vodafone's stance is less clear. This is from a BBC Click article which, to be fair, is a couple of months old now.
Not sure about Orange charging extra. I tether my android mobile to my laptop by usb and can use it to access the internet. I can also use my phone as a wifi hotspot (it uses up the battery a lot) and connect my ipad. I haven't been charged extra by Orange perhaps because I have an uncapped data allowance.
This thread is now locked and can not be replied to.