NBX 100 - Stop set from ringing while on the phone

[surfsailor]

Have a NBX 100 system. I am wondering if there is a way to stop the phones from ringing while you are talking on the handset. It is quite annoying to be talking with the handset or on speakerphone and if you are being called or you are part of a hunt group that is being called, the ringing disrupts your call.

Is there a way to set the system to stop your phone from ringing while you are talking on it ?