Just upgraded my German unlocked GSM Pre to webOS 1.3.1 (US) from webOS 1.2-Sprint, 'over the air'. 1.2 just said update available, and I clicked on update now. Device info now mentions: Palm webOS 1.3.1. , configuration Sprint 2.0. The phone preferences now has a Manual Settings entry. If enabled an Edit Network Settings entry appears. From that one, a form for an Internet APN and a MMS APN can be filled out.
After the update I did not have a 2G/3G data connection. I upgraded the manual settings for Tmobile-NL: APN internet Username tmobile Password tmobile . And it worked (have to 'save' these setting though, by going back to settings!) . I have 3G data again.
This leaves the question whether activation also has a opportunity for changing these setting . I don't know since the upgrade did not require a new activation.