GSM Codes with Osmocombb

Hi, I'm playing around with Osmocom for a while now. My final goal is to use it as a stationary phone on a PC to be able to remotly control the phone. I checked out the sylvain/testing tree, to use my SIM card and managed to be able to make and receive calls. Very amazing so far. :-) Now I tried to send GSM codes (like *#21#, oder *21*{NUMBER}#) to set and unset call diverts. It seems, that "call 1 *21*{NUMBER}#" does not work. Normal GSM cellphones seem to handle these codes not as a normal call. Does anybody know how one could send GSM codes to the network? Thanks Tim