I am going to be London and want a Sim card primarily for data. Are there any stores for sim cards in Heathrow? Thanks! Bryan
Yes, just as at every other major airport in the world.
There's a Vodaphone store outside security on the checkin level at Terminal 5.
Be careful of the SIM cards sold at the airport, they are more often more expensive. Elsewhere you will find free SIMs, you just load them with a plan from your chosen carrier. Also not all plans are equal! To get the best deal go to an independent store who will advise you on the best carrier for your needs eg Carphone Warehouse or Phones4u. Their staff are very knowledgeable and helpful and the stores seem to be on every street corner! http://www.carphonewarehouse.com/ http://www.phones4u.co.uk/
And, of course, your phone needs to be unlocked from your carrier or a replacement SIM won't work.