BT has agreed to buy the UK's largest mobile operator EE in a cash and shares deal worth £12.5bn. The deal, which BT said would create the UK's leading communications provider, will be partly financed by a £1bn share issue.
The mobile network has an 11% market share in Northern Ireland.
Following the transaction, EE's current owners Deutsche Telekom and Orange will hold stakes of 12% and 4% in BT. Deutsche will be entitled to a seat on the board.
BT chief executive Gavin Patterson said: "This is a major milestone for BT as it will allow us to accelerate our mobility plans and increase our investment in them."
The group had announced in December that it was in talks to buy EE.
BT said the transaction was subject to approval from shareholders and clearance from the Competition and Markets Authority.
It is buying what is currently the UK's leading network, with 24.5 million direct mobile customers.
However, this position is under threat as Hutchison Whampoa, owner of rival Three, is in talks to buy number two operator O2.
That would increase the proposed joint network's market share in Northern Ireland to 69%.
Meanwhile, BT said that it expected to achieve operating cost and spending synergies of around £360m a year with its EE deal.