I recently tethered my HTC Mogul (Sprint) to my N800 through WiFi. There is a way to hack the Mogul so that it acts as a router and accepts incoming connections from multiple sources, bridges them to the EVDO-Rev A radio and out to the internet. It's just an ad hoc Wifi connection just like Bluetooth, but obviously it's not Bluetooth.

Google "WMWifirouter" or "Windows Mobile Wifi Router" which works on a few different types of WM phones.

I was actually able to put the Mogul in my work bag, connection the N800 to it with Wifi, and stream Internet radio while driving at 60 MPH on a bus. Not one single hiccup.