Vodafone and O2-owner Telefonica are to work together to speed up the delivery of 4G services in the UK.
The two companies will continue to compete but will pool their infrastructure to operate and manage a single network grid across the country.
The companies said the move will see 4G mobile services, which will allow users to download music and film to their phones at the same speeds as home or office computers, delivered up to two years ahead of Ofcom's requirement of 98 per cent coverage by 2017.
Guy Laurence, Vodafone UK chief executive, said: "This partnership will close the digital divide for millions of people across the country and power the next phase of the smartphone revolution."
The two companies, which have an existing joint partnership called Cornerstore, which covers some 4,000 sites, will retain complete control over their wireless spectrum and will continue to compete with each other in all products and services.
The new agreement will merge all infrastructure into one new company - Cornerstone Telecommunications Infrastructure - that will also be able to offer indoor 2G and 3G coverage targeting 98 per cent of the UK population by 2015.
Under the proposals, both companies will have access to a single grid of 18,500 masts representing an increase in sites of more than 40 per cent for each operator.
The joint venture will also be responsible for the building of new sites needed to extend coverage into rural and remote areas.
Each operator will, over time, take responsibility for the design, management and maintenance of the radio equipment as well as local transmission in one half of the country.
Telefonica UK will manage and maintain elements in the east of England, Northern Ireland, most of Scotland and north London, while Vodafone will cover the west of England, Wales and south London.
Both companies are currently engaged in discussions with Ofcom and intend to establish the joint venture and network sharing arrangement later this year.
Ronan Dunne, Telefonica UK chief executive, said: "Exceptional customer demand for the mobile internet has challenged the mobile industry to consider innovative solutions to building a nationwide network that will be fit for our customers in the future and support the products and services that will truly make Britain digital."