We recently traveled to Crete for a week-long vacation. In preparation, I read the ATT Wireless website's suggestions for controlling charges while traveling overseas and called ATT. I already have the free notation to my number that I can have access to phone-roaming while overseas, something that I set up awhile ago. And then, as I have for other trips out of the US, I purchased the 20mb data package [$30], so I could get my emails and download and upload easily up to that 20mb limit [it costs much more after that point].
Fortunately, I found when I arrived that in many places [the airport, hotels] I could get online through wi-fi free of charge. So, I ended up mainly finding a hotspot, getting online through wi-fi, getting emails, uploading and downloading information and items, and having no problems sending and receiving messages and information. At the end of the trip, my total data usage is about 350kb up and 4.3mb down, much less than my package allowed. In the past, I have been able to cancel the package and everything is prorated. You can't do it too fast, or charges not yet submitted to ATT will not fall within the package deal, but in a few days, after checking my wireless bill online, I should be safe to cancel the package, get a credit for unused use and the rest will fall under the mb purchased.
The other suggestion ATT makes, which is wise to remember, is to turn OFF Data Roaming, so even if you are up and running and your phone system is operational, data is not being sent/received without your knowing.
I should also note that the phone service was excellent. We had to make several calls in country to find lodging and make other arrangements and had no problem at all, either making or receiving calls. And then, after I had downloaded recent RSS Feeds via my NetNewsWire application, I could read them offline and keep up with the latest news.