The Guardian is reporting that UK former-monopoly BT has been having discussions with T-Mobile and 3 about launching a mobile-phone network.
The discussions are described as "at an early stage", but apparently involve both existing mobile operators working with BT to launch a mobile network, something BT hasn't owned since spinning off Cellnet back in 2001. Cellnet later rebranded as O2, and got bought by Telefonica two years ago.
It's worth noting that T-Mobile and 3 already share radio networks, so the idea of both companies being involved in the deal isn't as unlikely as it sounds. Vodafone and Orange also have a network-sharing deal, though in their case the network is run by a third party that counts both operators as customers: a setup which would lend itself more easily to incorporating a new network.
There isn't much in the way of spectrum available for a new 3G network, so anything BT launches will have to piggyback on spectrum owned by other operators - which makes sense as even BT wouldn't want to be rolling out a new national transmitter network in this economic climate.
So even if BT does launch a mobile network it will be little more than an MVNO (Mobile Virtual Network Operator), which the telco already tried with Vodafone and the ill-fated "Fusion" product. So while investors might like the idea of BT having its own mobile network, there really isn’t much of an opportunity - unless BT decides to do something completely mad, like buying 3. ®