My only guess is that for some reason Treo is using some sort of standard built-in DUN rather then PDAnets version. You wouldn't be able to authenticated with the standard Treo/VZW DUN. But honestly I really have no experience with Treos/Palm/PDAnet. Could it be the Palm version of PDAnet doesn't offer up BT DUN services? Just connecting via BT sync with a PC?

It might be worth a shot e-mailing June Fabrics to tell them what you are trying to do. They've been very resposive to me in the past.