Why don't you use PDANet http://www.junefabrics.com/palmnet/ on your Treo?

I installed it, but I could not find that it had any purpose other than to use the Treo as the modem for a Windows computer that has PDANet installed on it. It doesn't appear to make Treo become a modem that will work for some other computer (or Nokia 770) that doesn't have PDANet installed.

I have PDANet for WM5. With this version, you can connect with your 770 (or a Mac, for instance) using bluetooth DUN. You just need PDANet on the phone. I just activated BT dun via PDANet and then I paired the phone and my N800.

I wonder if this would work on the treo? (I used to have a 600, but that device didn't have BT).

I'm trying, but I still do not find anything that indicates PDANet can do this. You can connect the Nokia 770 to a bluetooth DUN phone without PDANet (it's just not as easy). The reason something extra is needed on the Verizon-branded Treo 650 is because the Verizon-branded Treo 650 has DUN disabled. PDANet makes it work with a computer that has PDANet installed on it, not anywhere else. And it says "only runs on Windows XP/2000/ME/98SE and does not support Mac." If their software can do this, they sure do need to work on their marketing text and other documentation. Remember, I downloaded and installed it and read its instructions before coming to this conclusion.

I tried it again, just to make sure. Connects my Treo 650 to my PC, just great, but still doesn't make bluetooth DUN work on the Treo 650 for another device to attach to it.

With this bluetooth modem thing, do you have to have an internet subscription? I mean, do you just plug it in the phone line and have internet through blue tooth? How does it work?

Yes, you have to have an account with a dialup internet provider. I have Verizon DSL, and pay the extra $15/mo. for the nationwide dialup access...my husband's a pilot so he needs access in hotels that don't have wifi.