Prepaid Sim Card

I have an ipad2 but presumably my experience applies to your iPad. The staff at the London store where I bought the prepaid sim (Three) changed the SIM cards. My iPad recognized the new service immediately and I was in business. If there's a need to do anything else I would let the staff handle it so you'll know it's working before you leave the store.

SIM cards are sold in vending machines, but I agree that buying one in a shop and letting them install it is best and easiest. Phone shops are everywhere. I just walked into the first one I came across and bought a prepaid plan for the duration of my trip. They installed the SIM in my phone and set it up. Took about 15 minutes. Most phone shops seem tied to a specific network provider, but some aren't. I doubt the choice of provider is important for a typical visit, but the providers do offer coverage maps on their web sites. I remember seeing some differences in some locations in northwestern Scotland, but everyone seems to have blanket coverage elsewhere.

Tex is right - if you're buying the SIM at a store, make sure the staff there activates everything before you leave. But if you're buying it at, say, a supermarket, where there's no "staff" to help, you'll find that it comes with all the required numbers. The SIM is usually attached to a credit card-sized larger card (you punch it out of this larger card), and on the larger card are the SIM PIN, SIM PIN 2, and some other numbers - all identified. So, if you are asked to put in any numbers, just look at that card.

Thanks, to all of you, I really appreciate the helpful advice!
Carmen