O2 has launched an app to allow its users to make and receive phone calls and texts via a tablet, computer or smartphone, without the purchase of credits.
Available for Android, Apple's iOS devices and Windows 7 PCs, the Tu Go app deducts charges from a user's existing call minutes allowance, unlike Skype and other chat apps which involve the purchase of credit.
The app is, however, limited to "pay monthly" subscribers but does not require both parties in the conversation to be using the software, only the caller to have launched Tu Go.
The move comes as O2 aims to challenge Skype and other Voip apps, which traditionally require users to purchase credits to make calls on different devices.
Product manager Caroline Dundas, commented on the launch: "Customers can now take their mobile number wherever they like, even away from their mobiles," she said.
Dundas went on to liken the service to the way email developed: "In the early days you could only access email from the machine it was installed on but then web mail came along and that allowed you to access messages from any device," she said.
"This is opening up comms in the same way."
Tu Go has been available through Apple's iOS store since October last year, but had previously restricted its functions to about 1,000 testers.