I want to know if I can call a GSM modem (a SIEMENS MC55) from a normal analog (PSTN) modem. If so, how do I have to configure the GSM and the analog device? I've read about the +FCLASS and +CSNS commands but the connection doesn't work - I'm getting a BUSY or NO CARRIER. Are there other requirements?
After extending the initialization string of the GSM modem with 'AT+CSNS=4' the device was able to connect with analog modems.