I was just out of the USA for a few days and received a $126 data roaming charge from T-Mobile despite the fact that I did not actually use the phone at all except for WiFi and calls.
If "Data Roaming" is checked in the settings you will be charged eveytime the phone connects with a network. I would strongly recommend that you turn this off if you are outside of a T-Moble network, apparently and according to their customer service, you will be charged a extra data roaming charge in the USA if you connect to another carriers 3G network!!
T-Mobile had a very hard time understanding the difference between WiFi and data roaming but to be fair they did credit half the charges when I complained. Thankfully I was only out of the country for 4 days... (I even had charges from the Airport where I had a two hour layover)
If "Data Roaming" is checked in the settings you will be charged eveytime the phone connects with a network. I would strongly recommend that you turn this off if you are outside of a T-Moble network, apparently and according to their customer service, you will be charged a extra data roaming charge in the USA if you connect to another carriers 3G network!!
T-Mobile had a very hard time understanding the difference between WiFi and data roaming but to be fair they did credit half the charges when I complained. Thankfully I was only out of the country for 4 days... (I even had charges from the Airport where I had a two hour layover)