OK, so I've searched this thread and found lots of information on obtaining a US SIM card for my UK phone to use on a forthcoming trip to the US. I just need a little more advice. I will be transiting at JFK. I will then be spending time in PR, GA, and AL. What would be the best service provider for this trip? Is there one that offers better coverage for this?

Also, I've seen some US SIM cards available for sale on ebay. Is there any disadvantage to purchasing this was rather then directly from the store (apart from the obvious/usual ebay risks)? Otherwise, is there somewhere at JFK to purchase one? If not, it would be ideal to be able to have this delivered to me in the UK so I can activate immediatly on arrival at JFK. I will mainly be using the SIM to text abroad so heaps of minutes is not a priority (however I will be making some calls).

Thanks in advance for your infomation!