When I dial an external number using either the SIP phone (Yealink T46S) or the 3CX softphone I can not hear it ringing, there is just silence. It does however ring at the other end and if the call is picked up the audio works just fine. When I call between extensions I can hear the ringtone so that I know that it has established the connection. The firewall checker shows everything green. I'm not sure what could cause this.