The following lines in ~/.osso/call-ui.ini do the trick: [supplementary] ssc=1 Please note that officially this feature does not exist and therefore does not come with a warranty of any kind. The settings applet (Settings > Phone) does not properly indicate some of the services and does not allow revoking all of them. Only modify the .ini file if you are feeling experimental and already know your way around the MMI codes.
I haven't checked if someone has opened a bug regarding SS codes yet.