Bellow is a block diagram of how the BerryGPS-GSM can communicated with a Pi.
There is a serial switch which controls how the GSM and GPS modules speak to the Pi.
By default, the GPS speaks via serial to the Pi serial pins and the GSM only speaks via USB.
You can change how this works. There are jumpers for Serial Switch (JP1/JP3) on the back of the PCB. These jumpers can be used to change what component is connected to the Pi serial interface.
Soldering jumper JP1 closed will connect the GSM module to the Pi serial interface. The problem with this is that now you cannot communicate with the GPS module.
If you really want to free up the USB port, you would need to switch between GPS and GSM using the serial switch as both GSM and GPS cannot speak via serial at the same time. You can use any GPIO pin connected to JP1 (you would need to solder a wire to JP1). E.g. switch from GSM to GPS every 40 seconds to get location and then switch back.
Mark --OzzMaker.com --