R – How to determine the type of Windows Mobile device

It's perfectly possible. Just start a bluetooth server registered with the HID service Guid {00001124-0000-1000-8000-00805f9b34fb}. If the device supports the Microsoft bluetooth stack you can use Peter Foot's excellent .NET CF library (http://32feet.net/) and BluetoothService.HumanInterfaceDevice;

UPDATE:

With Peter Foot's library the server would look something like this:

using System.IO;
using InTheHand.Net.Sockets;
using InTheHand.Net.Bluetooth;

// ...

BluetoothListener l = new BluetoothListener(
    BluetoothService.HumanInterfaceDevice);
using (l) {
    BluetoothClient c = l.AcceptBluetoothClient();
    using (c) {
        Stream s = c.GetStream();
        using (s) {
            // send HID bytes
        }
    }
}

Regards, tamberg

As a suggestion you could always try using the OpenNETCF serial port library. It's interface compatible and that way you have all of the source down to the device manager calls, so you can see why any errors might be thrown.