British telecoms giant BT has agreed to buy the UK's largest mobile carrier, EE, in a deal worth $19 billion (£12.5 billion). The deal means BT now has access to EE's 31 million customers and the largest 4G customer base of any operator in Europe.

A deal between BT and either EE or O2, the UK's second-largest mobile carrier, has supposedly been in the cards for several months. In December, it was reported that the telecoms company would announce the takeover of one of the companies before the end of 2014. The delay also came with a rise in price — at the time, the deal was expected to be worth $15.2 billion (£10 billion).

EE is the UK's biggest mobile carrier

BT made its intentions to re-enter the consumer mobile market in 2013, when CEO Ian Livingston confirmed that BT had invited tenders from UK carriers to form a 4G partnership. EE was a particularly juicy target. The mobile operator successfully bolstered its 4G userbase by 2 million in the last financial quarter, pushing it from 5.7 million customers to 7.7 million. In March last year, BT cemented its relationship with EE, confirming a deal that saw EE provide mobile virtual network operator (MVNO) services to BT customers.

The telecoms giant sold its shares in O2 in 2002, but BT has now come back to the mobile market in a big way. As a result of today's deal, it wields the largest 4G network in the country to go alongside its broadband, landline, and TV services.