This only really applies when you are using a verdex motherboard with a GPSstix daughterboard.
The GPSstix board was originally developed for the connex and basix boards however are compatible with the verdex boards. The only change is that the verdex has one less serial port (no HWUART), instead the BTUART lines (ttyS1) are routed via the GPSstix's HWUART pins so when you are connecting a serial device you need to connect it to the pins marked HWUART on the GPSstix and enable the BTUART on the gumstix.
On the gumstix to enable BTUART you need to make sure that GPIO 42 and 43 are set up correctly:
Now you should be able to communicate using ttyS1.