I've talked to people in the last three weeks who report that T-Mobile US SIMs are working with the US APNs while roaming on other T-Mobile networks. Specifically, UK, Germany, and NL.

They (T-Mobile) still claim to be charging $10/MB while roaming. I was on Cingular's pre-T-Mobile network in NV a few months ago and was not charged for any data while I was there.

-alan in seattle