The purchase, which still has to get regualtory approval sees BT pay with a combination of cash and new ordinary shares issued to both Deutsche Telekom and Orange.

BT said in December it was in exclusive negotiations with Deutsche Telekom and Orange to acquire the mobile operator, which had 31 million customers at the end of 2014, of which 24.5 million were direct mobile customers and 834,000 were fixed broadband customers. Another 3.7 million were MVNO (mobile virtual network operator) customers and 1.9 million were machine-to-machine connections.

BT Tower Image: Flickr Taro Taylor
BT Tower Image: Flickr Taro Taylor

Carriers in Europe are keen to combine their fixed, cable and wireless offerings for synergies and economies of scale and to cross-sell to customers a bundle of services.

Hutchison Whampoa, owner of the 3 network, said in January it is in negotiations to acquire O2, another mobile operator in the U.K. EE, O2, 3 and Vodafone, yesterday committed to improving the UK's mobile coverage wuth a binding agreement with the regulator Ofcom.

BT said the transaction complements its "long-term network vision to build a single, seamless, converged platform, supported by a single IP network, that is able to serve customers with no distinction between fixed and mobile."

After the transaction, Deutsche Telekom will hold a 12 percent stake in BT and will be entitled to appoint one non-executive member of the BT board of directors, while Orange will hold a 4 percent stake.

BT said  the cash return on investment of the purchase was expected to "comfortably exceed" its cost of capital in the third full year post Completion