Tesco is has launched a new service that enables Wifi mobile phones to make free VoIP calls to and from anywhere in the world.

The TalkWifi service currently supports only Nokia's N95,N81, E65 and E51 handsets but more models will be added by the end of the year. It is an extension of Tesco's existing Internet Phone service.

VoIP calls to other Tesco users are free; Wifi calls to landlines cost 2p a minute and 10p a minute to any UK mobile, regardless of network.

The system uses technology from the Australian company Freshtel, which supports the SIP standard for web calls, but it seems that VoIP calls may only be made to other Tesco users. We'll be checking that out when we review the service.

Any users of supported phones can join the service by texting 86688 with the word Talk.