For your information:
Using the MC7710 in direct IP mode on linux kernel 3.2 (driver 1.7.40):
- 5 serial ports are attached: ttyUSB0 - ttyUSB5
ttyUSB3 -> AT command port
ttyUSB2 -> NMEA port
To get gps data through the NMEA port i had to send $GPS_START to it after sending the AT!GPSTRACK command to the AT command port.
Thanks to Bjørn for his hints.
Tobias