I followed the instructions that the voip provider (Callcentric) provided and even updated the 3cx software which now includes specific Callcentric support. However, I kept getting a 403 error saying line authentification failed if I was connecting using the 3cx client with my login settings set to using the system server - which is what I want isn't it. I copied the settings from when the extension was set up. However, if I reset my login settings to use the SIP server then the line shows up green. Moreover, the auth id must be my user login name not the SIP no. Changing the auth id to username side has no effect. I have deleted also the extension password. Whatever I do I am unable to call out.