Travel Advice for Eli 20.0!

When Eli 20.0 goes to the UK at the end of September, what are his best options for cellphone service? Apparently, Verizon (his current carrier) is a bad choice. Is he better off starting service with a UK-specific carrier when he arrives, or is there some other strategy he should use?

If you've gone from the U.S. to the UK for an extended length of time, and have sound advice on this topic, please let me know. 

We played golf on a heinously slow Sunday, and in-between shots he was reading a book from his massive reading list for his International Politics between WWI and WW2 course. 

Grinder.