Tesco has today launched a new Wi-Fi service for mobile phone users that allows customers to make free phone calls regardless of which country they are calling to or from.

Tesco TalkWiFi is available as a downloadable app for Nokia phones and enables customers to make free calls from a Wi-Fi hotspot to recipients who are also within reach of a wireless network.

Demonstrating the service, Tesco's project manager for Tesco TalkWiFi, Nick McGlashan, told us he had trialled the service while on a business trip to Australia. Using the service, he was able to make calls to the UK of up to 59 minutes duration without incurring any call charges.

Contacts from both the phone handset and SIM card are automatically imported to the Tesco TalkWiFi contacts list and dynamically updated thereafter.

Callers who are within a Wi-Fi area are shown as a green IM-style icon on this list. The handset owner immediately knows whether they are in a Wi-Fi zone as they are shown as a green avatar at the top of the contacts list. If a call starts out as a free Wi-Fi to Wi-Fi call and one or both of the callers strays out of a wireless area, the call immediately drops.

At the start of a free wireless phone call, there is a short announcement stating that the call will be free. Tesco's McGlashan says the idea behind the service was to make setup and use as simple and straightforward as possible. Glashen and his team have been working on the development of the service for the past year and a half.

The Tesco TalkWiFi service is an extension of the existing Tesco Internet Phone service which combines standard landline and VoIP broadband phone calls.

Although broadband phone calls aren't wildly popular in the UK, Tesco says its Internet Phone service is in the top five of such services (Skype is the best-known provider of them).

Unlike the Tesco Internet Phone service, which is dependent on a landline and fixed-line broadband access, Tesco TalkWiFi uses mobile phone handsets. However, pricing for the two services will be identical, with non-Wi-Fi calls costing 2p a minute to landlines and 10p a minute to a mobile phone on any network.

Tesco is launching the service with four of the most popular Nokia handsets, the N95, N81, E65 and E51. Support for more handsets will follow shortly. A Tesco spokesman explained that Nokia's handsets had been chosen because of the proven robustness of the Nokia Wi-Fi stack.

Setting up the service involves sending a premium-rate SMS text to 86688 with the word Talk. A few minutes later, a text message will arrive with a link to download the necessary application. The cost of the initial SMS is automatically credited to the user's account. Accounts can be either prepay "anonymous top-ups" or on a Tesco phone contract. Vouchers to top up accounts with credit can be bought at Tesco supermarkets.