When I first started playing around with SIP trunks and registering it. Had issues and with help, reading and playing around with the configurations. This is what I found. I decided I should share this since I have seen a few posts about configuring SIP trunks. The below configuration is only for credential based SIP trunks. The other SIP trunk is IP address based, where the calls are validated at the SIP providers end is by the Public IP.
Please find the configurations steps below if you have multiple direct dials and would like to display each number when
the call is made. e.g. extension 2001 with Direct Dial of 01xxxxxxx2001 calls, he wants that number to be displayed.
If the below mentioned configuration is used, ensure that translation rules are in place, since the SIP provider looks
for a number that is part of the trunk to validate the call.