More than ten years after it sold its shares to O2 and exited the consumer mobile market, BT may soon make a comeback as a UK carrier. The company announced today that it has signed an multi-year agreement with EE to use its 4G services to support both its customers and employees. While the company remains quiet on whether it plans to add mobile services to its existing media packages, BT CEO Ian Livingston remarked earlier in the year that it was "highly possible" that we'd see BT-branded 4G SIM cards bundled alongside its TV, broadband, fixed-line telephone and public Wi-Fi services. Let's not forget the fact that the telecoms giant also spent £186.5 million securing its own 4G spectrum. BT says it will focus on moving its existing clients over to EE's networks while expanding its "strong Wi-Fi presence" in the UK, but we believe it won't be too long until EE, O2, Vodafone and Three have some competition.