Use mgetty to answer a call and press a key

I bought a GSM shield for the Raspberry Pi (version 1, B) and a SIM card to join the proper cellular network. I use mgetty to react to my call, like this: mgetty conf which works just fine and the script executes once I call the RPi: port ttyAMA0 speed 9600 post-init-chat "" ATH0 OK ATS0=0 OK AT+CLIP=1 OK rings 2 answer-chat "" ATH0 cnd-program /home/pi/caller.sh The thing I want to do is not only executing the script above (which is currently a dummy script), but also answer the phone call and press a specific button (press *). Interestingly, there is quite some documentation across the web, how to use mgetty as a dialin modem, but I couldn't find a way to answer the call and send a key. Even this question is unanswered and I cannot post a comment to ping the author of the question...