My wife and I have an unlocked 6 and 6s, both currently on US based T-mobile pre-paid plans ($40 each for unlimited talk, text, and 3GB of LTE per month). We are both going to London for a couple weeks later this spring. What are the best approaches for getting high speed data service while we are there? We don't need a local London phone number, or expect to make many voice calls while there. Appreciate any insight - thanks!