In 2010, T-Mobile merged with Orange to form “Everything Everywhere” (EE). In 2014, the T-Mobile brand is being gradually phased out. They still offer some 3G-only service including “The Full Monty” (unlimited internet with no download limits). For 4G internet, you’ll now need to choose a tariff from EE.

Orange and T-Mobile launch “Smart Signal Sharing”
April 29, 2012
Orange and T-Mobile begin 3G network sharing
October 23, 2011
Orange and T-Mobile customers: Register now for enhanced reception on merged network
October 5, 2010