I had the same problem with my HTC PPC 6700 running Windows Mobile 6.1. Microsoft took DUN out of Windows Mobile 5+. PAN works using Internet Connection sharing. And if your phone has Wifi, you can even set it up as a Wifi router that your N810 can connect to. See these two threads I started for directions: Bluetooth DUN on a HTC PPC 6700 & N800 Higher Speed WM Phone Tethering Than DUN