BT's Bluephone must be convergence without the con

It's been a long time coming, but BT is finally gearing up to launch its Bluephone system. On paper, it looks good: one phone that works on fixed lines in homes and offices and elsewhere as a mobile, saving you the need for two handsets and two bills. In practice — who can say. BT has yet to reveal how much it will cost the user, nor has it divulged other details such as whether incoming calls will be priced on a mobile or fixed-line tariff.

Leaving such quibbles aside, Bluephone is an experiment in convergence that deserves to be tried. Other, similar attempts at using mobile phones in office and domestic environments haven't worked out too well — who now remembers Nokia's InSite picocell base station? — and VoIP software running on smartphones can do a pretty good job of low-cost alternative call routing, but if BT cracks convenience, choice and features it will be an exciting invention.

It could also be the first step beyond the much-promised triple play where one service provides video, voice and data down one line, adding mobility to make a four-way mix. Users, the industry and commerce in general need that sort of innovation.

Yet we also need competition. While there's nothing wrong with BT trying to become an integrated fixed line and mobile provider, there are problems if it's using its inherited dominance in traditional telephones to exclude other operators from playing the same game.

So far, the mobile networks not connected with Bluephone have been very cool on the idea: Ofcom needs to satisfy itself that this is not because the price of entry is being kept artificially high, and that BT is not planning to make switching away from Bluephone unfeasibly difficult for its customers. Lock-in and exclusion are two of the more dangerous weapons telcos use to maximise their revenue, and a converged system has great potential for both.

Regulation always trails innovation. In a case as important as this, Ofcom must get the right numbers.