We purchased 30 of the Sierra Wireless MP595W modems and they work perfectly with the GPSGate Server. These devices are very cool. Ours are setup with EDVO through Verizon Wireless and we use the built in WIFI hotspot as well. We currently have them configured to send in TAIP.
I have not been able to get the IO and Analog inputs configured and do not know if this device is compatible with GPSGate. I am working with it more this week and will post back.