BT plans to launch a Wifi-enabled mobile phone next year that will allow people to make cheap international calls from wireless hotspots across the world using Voice over IP (VoIP).

The phones could threaten the revenues of mobile operators by offering a cheaper alternative especially in the home, from where an estimated 30 per cent of mobile calls are made. However, BT itself could benefit from an increase in fixed-line charges.

BT has also launched a service called the Broadband Voice, targeted at small businesses, using a Fujitsu FX-840 adapter that plugs into a broadband connection and allows ordinary phones to be used for VoIP.

For £5 a month, users get two extra 'virtual' lines with VoIP-reserved 05 numbers and cheap call charges for a maximum 10p an hour for national calls.

The adapter also allows you to make and take calls anywhere in the world using the same number. But, in both moves, BT faces stiff competition.

VoIP pioneer Skype already offers a client allowing VoIP calls to be made from Wifi-equipped Pocket PC handhelds across the world and calls to fellow users are free.

Calls to standard phones are cut-rate. Routers and adapters are already available allowing normal phones to make calls over the web and, again, VoIP to VoIP calls are free.

For more on how to slash your phone bills by using VoIP to make cheap or free calls over the Internet, including reviews of a range of phones and services, see the free supplement on the latest edition of Personal Computer World, out November 18.