Ever since BT invested in Fon, I’ve been on the lookout for the launch of a joint BT/Fon service in the UK, and as expected, word of the launch of ‘BT Fon‘ , creating the world’s largest Wi-Fi community, has just hit the wires.

The partnership between BT and Fon is very ingenious, bringing together BT’s 3 million Total Broadband customers, most of whom already have a wireless router in the form of the BT Hub, and Fon’s 500,000 members. Members of the BT Fon community will be able to access any of Fon’s 190,000 Wi-Fi hotspots worldwide, as well as the new BT Fon hotspots that will be created.

The new BT Fon hotspots are what makes this proposition special. To use BT Fon, users have to agree to share a small portion of their broadband connection with other members. BT will quite clearly be encouraging its users to opt into the service, and given that BT is the largest ISP in the UK and that each router has a range of 50ft+, BT Fon could very quickly provide complete wi-fi coverage within cities and other built-up areas.

Gavin Patterson, BT Group managing director, Consumer, said:

“This is the start of something very exciting for BT. Today we are launching a people’s network of Wi-Fi, which could one day cover every street in Britain. We are giving our millions of broadband customers a choice and an opportunity. If they are prepared to securely share a little of their broadband, they can share the broadband connections of 190,000 others without paying a penny.”

To provide even more coverage, BT Total Broadband customers will also be able to use BT’s existing BT Openzone wi-fi network, as well as 12 wireless cities. I asked Fraser Smeaton, the Senior Propositions Manager who lead the launch what the coverage targets would be for BT Fon, but he declined to answer. I’m fairly certain that it’s going to be high, as I sometimes used to leave my Dell Axim Wi-Fi on whilst I was driving, and I was amazed by the number of potential wi-fi networks I could have connected to.

Fraser Smeaton and his team didn’t give any details of how much bandwidth each BT Fon customer will be asked to share. It will probably be enough for BT Fon users to be able to surf the net, read emails, watch YouTube videos etc but not enough for anyone who wants to sit outside their neighbours house and download a torrent.

Developing a national Wi-Fi network is going to pose potential issues for mobile operators. For instance, if I were a BT customer (unfortunately I’m with Telewest Virgin Media) I would be able to use my BT Fon Wi-fi connection with my Nokia N95 to not only get much faster download speeds, but I would also be able to make VoIP calls without having to worry about my data costs (VoIP is chargeable on my T-Mobile contract). I’m sure that many people will be thinking the same, including business users who have GPRS/3G cards in their laptops, particularly as BT Fon will be free to BT Broadband users.

It will be interesting to see how mobile and broadband operators respond to BT’s continuing moves to deliver broadband access both in and out of the home. The mobile operators have already been reducing their data costs of late; lets hope that new services like BT Fon force them to make even deeper cuts.