BT's attempts to converge the worlds of fixed and mobile have suffered limited success, according to the telco's sales figures.
The telco has sold its so-called Fusion converged handset to just 40,000 customers since its launch in summer 2005.
Fusion cuts phone bills by routing calls over a fixed network connection when one is available, such as in the home, office or a Wi-Fi hotspot. The handset also works over the mobile network where a fixed connection is not available.
This kind of converged communciation device has been seen as an important part of the mobile industry's future. But despite continued advertising by BT, sales of Fusion have been limited.
"To date, Fusion has not been a runaway success," said Carrie Pawsey, an analyst with Ovum.
Other industry analysts were equally downbeat. Thomas Husson at Jupiter Research said: "It's not a significant number of customers. It will take time to take off, [and for BT] to offer a compelling proposition."
The analysts say that BT needs to improve the battery life of handsets, offer a greater choice of handsets and simplify tariffs to boost sales.
ZDNet UK asked BT whether it regarded its sales figures as a failure. A spokesman said in reply: "We are happy with 40,000 on the Bluetooth platform. We don't regard it as a failure." The spokesman said sales would soon take off due to three factors: use of Wi-Fi (which has now been introduced in place of Bluetooth); a choice of handsets (there are now three instead of one); and more advertising campaigns.
BT said on Monday that it would allow Fusion handsets to be used for cheap calls in its city-wide wireless networks, of which it is currently building 12 across the country.
The telco will complete the networks by the end of March in Birmingham, Edinburgh, Leeds, Liverpool, Cardiff, Westminster, Newcastle and Glasgow, through its Wireless Cities initiative. Four other city deployments will also be completed in that timeframe, but those city councils have asked BT not to reveal their identity.
BT refused to say how many people are using its Wi-Fi hotspots.