A user posted an important observation on the Bluetooth COM support in Windows Mobile 5 here on the microsoft.public.pocketpc.developer newsgroup. The problem is that while the system allows you to create virtual COM ports for all your paired devices which support Serial Port Profile, most of the time this will fail because the COM port you pick is already in use, on many devices you can have just 2 virtual COM ports. I've posted a few of my thoughts in the thread linked above, but while there are things that Microsoft can work to improve there are also a few things that developers can do to avoid the problem:-
- Don't rely on the control panel for setting up ports, use the RegisterDevice route (or BluetoothSerialPort in 32Feet.net) to just register a port for the duration you need it (and possibly reuse the same port name). This also allows you to use a different port prefix since few COMx: ports are available out of the box.
- Don't use serial ports. Unless you need your device to be accessible by a legacy app then you can avoid using virtual COM ports altogether and work directly with Sockets (again 32Feet.net will allow you to setup these connections easily). The downside with this approach is it applies only to the Microsoft Bluetooth Stack, as the programming model for the main alternative from Broadcom is essentially based around ports. However based on the first batch of devices released with Windows Mobile 5.0 the Broadcom stack is a lot less common.