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(Pocket-lint) - O2 has set up its own VoIP (Voice over IP) service, allowing customers to make calls via Wi-Fi from a range of supported devices.

Called TU Go, the new VoIP service will let O2 pay monthly customers place calls over the internet from Apple, Android, and Windows 7 devices, using a dedicated app - meaning you can make calls regardless of whether you have a mobile connection or not.

Working in a similar way to Skype's paid-for calling service, the advantage that TU Go brings to O2 customers is that you don't need a separate account and calls and messages are received as normal.

Using the TU Go app, O2 customers can make and receive calls, send messages and retrieve voicemail, so long as the device is connected to a Wi-Fi network. That means, for example, that you could be connected to a Wi-Fi network in your basement and still make calls and send SMS messages without cellular reception.

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If you forget your mobile phone that's not a problem, as you'll be able to fire up the app on your Windows 7 PC at work and retrieve your voicemail or send important messages.

After downloading the app, you'll have to authenticate the device (an SMS is sent to your mobile phone) and then the TU Go app will receive calls as if it were your phone. You can, for example, run TU Go on your iPad or iPod touch, bringing calling options to devices that normally wouldn't allow it.

You can use up to five devices with TU Go and, once the app is up and running, all the devices will ring when you have an incoming call.

"Tu Go lets you take a call on a tablet, pick up text messages on a PC and have conversations in places with Wi-Fi coverage but no mobile signal," said Sally Cowdry, marketing and consumer director at O2. "We're letting nothing stand between our customers and their number."

Calls made using the TU Go service will be charged at the normal calling rate on your monthly bill. The app is free to download and available now on iTunes and Google Play. Support for Windows Phone and BlackBerry will be coming in the future, O2 told us.

Writing by Chris Hall.