On T-Mobile, the cost is 1.5 cents/kb. If you only do mail, it's not that expensive, as you don't rack up a lot of charges just checking for mail. If you web browse, though, expect a pretty hefty bill.

Here's their international coverage list: http://www.t-mobile.com/internationa...geInternet.asp

As you can see, France, Germany, UK, Ireland, Italy any many other countries have data roaming agreements with T-Mobile.

Since I'm 5 years into a lifetime ban on AT&T Wirleless, I couldn't tell you anything about their service.