Hi, i got a very similar issue concerning TRB 140.
Up to present, we have been using a specific custom made protocol that transmits digital input changes from gprs modem to a data gateway, which in turn converts the data to certain IEC protocol for SCADA. We have made the software in C and it runs natively in the modem device. Now, the current modem family has reached its EOL and we need a replacement for it. TRB140 would suit really well into this picture, but i really need to have a decent interface description upon how to handle modem functionalities and read/write the GPIO from from C-code. Also, i will need to have some kind of configuration interface for our own SW, but i think .ini file would be a decent solution for that. I checked the SDK instructions link from the previous response, but there was just an empty page?
Actually, we do also have some other plans in the future, so in case we succeed with this case, there might be also other projects following with other TRB versions ( i.e. serial port use).