Google has launched an online service that allows iPhone users and those with Windows Mobile or Symbian phones to sync their calendars and contacts with their Gmail accounts.

Google Sync, which has been launched in beta, is hot on the heels of an announcement that Microsoft is planning to launch a similar service at next week's Mobile World Congress (MWC) in Barcelona.

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When users add a new item on their Google calendars from their computers, for example, that change will be pushed out to their phones. The reverse also works, where a person adds or deletes a contact from the contacts list on their phone and that change is automatically made to their Gmail contacts list. The service is similar, although narrower, than Microsoft's My Phone.

My Phone will also let users sync calendar and contacts lists between Windows Mobile phones and the web, but it will also back up other phone data including photos, videos, text messages, music, documents and tasks. Users will be able to store data like photos and videos online and share it with friends. It is limited to Windows Mobile users and is expected to be released in a limited beta in a week or so.

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Neither Google nor Microsoft will charge for the services, unlike Apple with its similar service. Apple's MobileMe syncs calendars, contacts and email between iPhones and PCs or Macintosh computers, and lets users share photos from their phones on an online site. MobileMe costs £59 per year.

Microsoft was quick to point out that Google's license of Microsoft's ActiveSync enables the sync with Windows Mobile devices.

For devices like Symbian phones that support it, Google used the SyncML protocol to facilitate the sync. SyncML is a standard protocol for data synchronisation maintained by the Open Mobile Alliance.

In a blog announcing Google Sync, Marcus Foster, product manager at Google Mobile, noted a couple of caveats. Google Apps users will require their administrators to enable Google Sync in order to use it.

He also warns users that Google Sync will initially replace all existing contacts and calendar information on the phone. His advice is for users to back up that information first.

See also: Google unveils Book Search for iPhone