I needed to enable the Extended command set by issuing AT!ENTERCND with the Password.
Then I was able to ussue the AT!UDUSBCOMP=5 command.
0 - HIP DM NMEA AT MDM1 MDM2 MDM3 MS NOT SUPPORTED
1 - HIP DM NMEA AT MDM1 MS NOT SUPPORTED
2 - HIP DM NMEA AT NIC1 MS SUPPORTED
3 - HIP DM NMEA AT MDM1 NIC1 MS SUPPORTED
4 - HIP DM NMEA AT NIC1 NIC2 NIC3 MS SUPPORTED
5 - HIP DM NMEA AT ECM1 MS SUPPORTED
The modem registered and enumerated only ttyUSB0 - ttyUSB3. But, it also registered a Network Interface (eth1) on which I was able to use direct ip.
Using the above procedure to connect the modem and after that issuing the following commands:
ifconfig eth1 up
ip route delete Default
ip route add dev eth1
I am connected to the Internet now.
Btw: In the meantime I upgraded my kernel to 3.11.0-rc7.
Thank you for your help.