I posted a question on 9/7 and did an experiment on 10/9-12 in the Netherlands--a place I've always been charged for data.

1. I assigned up for a BB int'l plan on 9/9.
2. Went to the Netherlands on 10/9 with a Treo 650.
3. On 10/9, I used the Treo for e-mail only with the wap.voicestream.com apn.
4. On 10/10, I used the Treo for browsing with the the wap.voicestream.com apn.
5. On 10/11, I used the Treo for e-mail only with the internet2.voicestream.com apn.
6. On 10/12, I used the Treo for browsing with the internet2.voicestream.com apn.

On my Tmo bill, I was charged for data for 10/11 and 10/12 leading me to conclude that the billing system uses the apn as a determinant of what qualifies as BB e-mail only.

P.S. In calling, Tmo, they credited those charges.

Bottom line: use the wap.voicestream.com apn if you're using a Treo.