Did you manage to sort this as I'm currently in the same boat.
Went to T-Mobile which worked perfectly but couldnt port my old BT Anywhere number to them. It would only go to Voda/O2 networks.
So went to Talkmobile, they assured me it would be fine. Yes got my new SIM and the number is ported across but 3G wont work. Called them and the system has the settings for the Pre and Pre+ in there but no send button to issue out the settings.
They are now checking with the tech folks.
I have a feeling I'll be returning this contract, getting another PAC code and going to O2 next (not that I want to as they are really expensive).
Either that or back to T-Mobile and just get all my business cards etc. re-printed.
You just mention you have a Palm Pre 2 to the folks at the carriers and they just go "you have a what??"