You don't say what system you need this done on.
I have never tried but my understanding the newer NEC system here in the US make it impossible to restrict 911 calls.

I know on the SV8100 9100 if all lines are in use and someone dials 911 the system will hook flash a busy line and make the call.

Carl Navarro is dead on about the law.
Think about, there is a emergency and someone on a restricted phone is trying to call 911 and seconds matter.

Last edited by dans; 04/05/16 09:20 AM.

We get old too soon, smart too late