Ok, here is my experience:

1. I have a N800 but I didn't had a Bluetooth enabled phone until a few weeks ago.
2. Today, I upgraded the N800 to Diablo. When the tablet rebooted, it asked me if I wanted to pair with a Bluetooth device.
3. I looked at my Palm Centro nearby, and said "Why not?". enabled Bluetooth in the Centro (keep it off people, it's a battery killer), and selected OK
4. The N800 asked me to select my country from a drop-down list. I selected Argentina
5. The N800 then showed a list of the 3 local cellular providers, I selected mine ("Telecom Personal")
6. It asked me to pair the unit and gave me a 4-digit PIN. I quickly changed it to a 8 digit pin :-)
7. The Centro was added as a trusted device to the N800 and vice-versa.
8. On the list of connections available, my Palm Centro shows up on the N800.
9. I can select that connection, connect, and browse, seamlessly.

I never had to select "modem" or do any other fancy configuration other than what has been described above.

Guess I'm just lucky?
FC
PS: I expected the Centro to show a small delay or show "connecting to GPRS..." as often happens when starting a TCP/IP enabled application, but there's nothing displayed... it sorts of does all the connections in the background.

PS2: I *WISH* the N800 browser could show a "packet meter" (bytes sent/received) somewhere (upper-right corner of the browser window would be nice, with sugar on top, please , to keep track of how much money we're burning while browsing over Bluetooth/GPRS...