3g allows callers to see each other
Mobile phone operators T-Mobile and mm02 have won approval from the European Commission to share networks for third generation (3G) mobile phones in Britain.
Europe's competition watchdog said the agreement would not prove anti-competitive.
But it excluded the top 10 British cities from the "roaming" deal between the two operators, and said it would only apply in smaller cities until 2007.
Roaming allows mobile phone users to switch automatically from one network to another.
Competition commissioner Mario Monti said: "This decision strikes the right balance between infrastructure competition in the 3G market and the immediate consumer benefit of faster and wider roll-out of advanced 3G services."
Mobile firms are increasingly looking towards partnerships in a bid to minimise their outlay and stem huge costs.
They paid vast sums to obtain 3G licences, which allow users to see each other and send video footage during calls.
But long delays and numerous technical glitches have hampered the widely-hyped launch - and operators' ability to reap the return on their investment.
T-Mobile, owned by Deutsche Telekom, is Europe's second largest mobile operator while mm02 is the smallest of the five European players.
The two firms asked for approval to share their sites in Britain and Germany in February and the Commission has so far only given its accord for the British part of the deal.
At a price
The UK's first mainland 3G mobile network, Hutchison 3, officially opened for business in March after a series of technical glitches.
But with an average price of £400 for a handset, the technology comes at a price.
Trade and Industry Secretary Patricia Hewitt made the UK's first public mobile video call over 3's new service to Stephen Timms, the e-Commerce Minister.
The government has been a strong promoter of 3G technology, having earned billions of pounds from the sale of the radio frequency licences.
"The possibilities are immense.
"It has the potential to revolutionise the way we communicate and I am delighted that UK businesses and consumers will be among the first to benefit from it," said Ms Hewitt.