International Travel and the iPhone

"One of the most interesting wrinkles in the iPhone 4S-which I review at length elsewhere-is its status as a "world phone." Unlike previous generations, it supports both CDMA (Verizon, Sprint) and GSM (AT&T, the rest of the world) wireless technology right out of the box. But there are some interesting quirks to this product that may please savvy international travelers."

Basically it means that if you are Sprint or Verizon subscriber, you may have a better International experience than those of us with AT&T, or at least a cheaper one. All you have to do is ask for an "International Unlock" of the SIM slot apparently (with Verizon after 60 days, Sprint already comes this way). This way its a bit cheaper to roam apparently, but you can't use the same phone number. Decisions decisions. Have you used international services with your AT&T phone? How was the experience for you? I'm sure it's not as simple as I'm making it out to be but since I've never done it, I am wondering just how well it works.