I came across an interesting problem. I have an RB411 (but tried a 912, too, no difference) and an MC7710 3G card.
I would like to forward GPS positions via 3G.
And it's almost working

The MC card is set to output NMEA data continuously (AT!GPSAUTOSTART). When I connect to it with serial-terminal (ch2) in ROS nothing happens and gps monitor doesn't work.
Whether its' in a mPCI or an external mPCI with USB it's the same thing.
But! When using an external mPCI connected to a PC I connect via hyperterminal (any port config, same as /port settings) and it dumps NMEA data (COM18).
At this point I can reconnect the USB cable to the RB, connect to it with serial terminal (ch2) and see all the NMEA data just fine, and /system gps monitor starts workign as well (enabled and ch2) and GPS data is coming!!!!
So what is it that the ROS doesn't do and hyperterminal does??!?!?!?