Microsoft® Mobile Development Handbook

GPS

All consumer GPS receivers output data over a serial port in a text format devised by the National Marine Electronics Association (NMEA). Prior to Windows Mobile 5.0, you needed to establish a connection to the attached device by a serial port, or a virtual serial port for devices connected by Bluetooth, to receive incoming NMEA data, and then parse it yourself. Windows Mobile introduces a centralized GPS service that the user can configure through the Settings menu on the device. Because only the system is connected directly to the GPS device, with this approach multiple applications can access the same GPS data at once through a virtual COM port or a set of API methods.

Unfortunately, the managed APIs for Windows Mobile don't include support ...