Hi,
Sounds like you have made all the changes needed ...
Don't have a T630, but do have a T610 and that works fine with DUN and Zaurus, so can't see any reason why T630 should be any different.
Have you checked the basics. Switch off/restart both Phone and Zaurus (reboot) jut in case something has got stuck.
I know sometimes, the bluetooth connection would misbehave if you had trouble with it already.
Also, might be worth deleting the Zaurus Pairing on the phone if you already have one and temporarily unhiding the phone.
Sorry I can't give more specific help...
Zuber