MOBILE telephone users received good news yesterday when Britain's major supplier announced plans to slash its charges. Vodaphone is to cut its tariff packages for digital and analogue consumer customers by 50% and claims it will introduce the UK's cheapest off-peak calling rates next month, starting from only 2p a minute.

On the same day, BT announced that a revolutionary combined mobile and domestic telephone is to go on general sale in Britain for the first time later this year. BT claims its OnePhone service, which combines a mobile handset with the domestic phone, is a breakthrough in telephone technology.

Vodaphone's main competitors, Cellnet, which is 60% owned by BT, Orange, and One-2-One, all insisted they still offered the best overall value-for-money packages. The moves were welcomed by the Telecommunications Users Association (TUA) which said they were ''good news for the consumer whether business or domestic users''.

TUA spokesman Steve Thorpe said reductions in overall charges by many mobile telephone operators had resulted directly from recent complaints by Oftel over high charges.

In March, Mr Don Cruickshank, director general of Oftel - the Government-funded agency which regulates telephone companies - accused Vodaphone and Cellnet of exploiting their position by charging too much.

The European Commission has launched a Europe-wide investigation into the high price of mobile telephone calls.

The Competition Directorate could force cuts in charges if investigations reveal wide disparities in the cost of calls between mobile telephones and those from fixed lines to mobile networks. Vodaphone's tariff changes, effective from June 1, are the second set of major price cuts introduced by the company in the past six months.

Vodaphone said the new offer would mean off-peak rates on all its digital and analogue consumer tariff packages being cut by 50%, from 10p to 5p a minute.

BT said its OnePhone service would go on sale to the public this autumn following the successful development of a version for business use last spring. A price has still to be set. While in the home, the BT OnePhone acts as a digital cordless phone which logs on to the fixed telephone network.

Once outside its 300-metre range, it switches to a mobile network and becomes a cellular phone. Customers are offered a new single number which reaches the BT OnePhone regardless of whether it is in domestic or mobile mode.

Mr Eric Guilloteau, general manager of BT Mobility Solutions, said: ''Up to now, the emphasis has been on making products smaller. We are now moving to an exciting, practical new dimension. We are making them fewer.''

According to BT, the development gives Britain a lead over the rest of the world. Scientists at BT's research laboratories have been working with Swedish company Ericsson to develop the technology.

A business version of the telephone is already being supplied to a number of large corporations and the success of this service led to the rapid development of a residential model. Ultimately, the OnePhone service is expected to offer access to E-mail, fax, and the Internet.