I needed to pick up a local SIM for a friend visiting the UK in a month or so, and the carrier of choice for me when it comes to a single country SIM in the UK is usually 3.
Their plain language approach and, now a new 15 pound a month plan for voice--300 minutes, text-3000 and all you can eat data for 30 days, is just plain, dumb, simple.
Buy the pack at a 3 shop, dial 444 on your iPhone, wait five minutes and your connected. Honestly, this is the type of plan AT&T needs to offer in the USA. Uncomplicated. No lines to wait in, no store check-in, just ask for what you want and go.