Talkland is an intermediary that buys airtime from Vodafone and its rival, Cellnet, and sells it to its users as part of a package with a car telephone or handset.
GMC made a loss of pounds 2.6m in the year to December 1992 but is expected to be profitable in 1993 before exceptional items. The company has 210,000 suscribers, divided between the Cellnet network and Vodafone.
A Vodafone spokesman said neither the management of Talkland nor Cellnet customers would be affected by the change in shareholding. 'We regard this as an investment,' he said.
Vodafone, which will pay for the stake by issuing more shares, has also agreed to lend pounds 29m to GMC for investment in Talkland.
The cellular service market has been through an upheaval recently, with many smaller firms taken over or forced out of business by cut-throat pricing.
Vodafone has its own service provider, Vodac, which has 250,000 subscribers. Last year Vodafone acquired Hawthorne Leslie - now known as VHL - which has 75,000 customers.
Cellnet has yet to make any large acquisitions but has links with service providers owned by its parent companies, British Telecom and Securicor. A spokesman for Cellnet said: 'Talkland has grown by being even-handed and we do not expect them to change that.'
Analysts said the Vodafone acquisition of a Talkland stake is an attempt to establish more control over the subscriber base. Hutchison of Hong Kong, which is due to launch a mobile telephone network in competition with Vodafone and Cellnet, is already one of the largest cellular service providers in the UK.