The first stage of the shared rural network will increase coverage in each of the UK nations, with 124 new sites in Scotland, 33 in Wales, 11 in Northern Ireland and 54 in England, the companies said on Wednesday.
Construction will start this year and is scheduled to be completed by 2024, they said.
The mobile industry and the government agreed last year to create a shared rural network, at a cost of 1 billion pounds provided by operators and public funds to improve rural coverage.
In this first stage, the operators will target areas reached by only one network currently.
A second stage to tackle areas where they is currently no signal at all will be funded by the government.
(Reporting by Paul Sandle, editing by Andy Bruce)