Ah, gotcha. Well, T-Mobile would be easiest; no swapping SIMs out. You'd have to make sure that all the countries you're going to be in are on their list of countries covered under their free roaming, though. And remember that the free data is only 2G and calls aren't free, just the data and texting. SInce it sounds like your usage is going to be very limited it could work out to be a good option for you, just be sure you know the fine print. The main beauty of going prepaid international SIM is that you can't screw up: if you try to do something that isn't covered or that you haven't deposited money for, it just won't work. If you're on postpaid T-Mobile, they'll start tacking things onto your bill.