Ahí van las imángenes de la solapa principal de VOIP Providers, seguida por la de configuración del número externo:

También pego a continuación el LOG resultante de esta configuración:09:26:30.671 [CM504007]: Next attempt to register 12345@BBTel is scheduled in 10 minutes
09:26:30.671 [CM504005]: Registration failed for: 12345@BBTel; Cause: 503 SERVICE UNAVAILABLE; from IP:200.112.128.83:5061
09:26:30.531 [CM504003]: Sent registration request for 12345@BBTel
09:26:30.484 Unknown system [CFGManager] tries to connect!
09:20:30.140 [CM504007]: Next attempt to register 12345@BBTel is scheduled in 10 minutes
09:20:30.140 [CM504005]: Registration failed for: 12345@BBTel; Cause: 503 SERVICE UNAVAILABLE; from IP:200.112.128.83:5061
09:20:29.937 [CM504003]: Sent registration request for 12345@BBTel
09:16:57.078 [CM504007]: Next attempt to register 10000@BBTel is scheduled in 10 minutes
09:16:57.078 [CM504005]: Registration failed for: 10000@BBTel; Cause: 503 SERVICE UNAVAILABLE; from IP:200.112.128.83:5061
09:16:56.968 [CM504003]: Sent registration request for 10000@BBTel
09:12:04.296 [CM504001]: Ext.99: new contact is registered. Contact(s): [sip:99@127.0.0.1:40600;rinstance=c122853f349c9a30/99]
09:11:39.796 [CM504001]: Ext.*1: new contact is registered. Contact(s): [sip:*1@127.0.0.1:40000;rinstance=6f177a688f2fe6b1/*1]
09:11:39.750 [CM504001]: Ext.*0: new contact is registered. Contact(s): [sip:*0@127.0.0.1:40000;rinstance=380a77149f028b1c/*0]
09:11:05.578 [CM504007]: Next attempt to register 11111@BBTel is scheduled in 10 minutes
09:11:05.578 [CM504005]: Registration failed for: 11111@BBTel; Cause: 503 Service Unavailable; warning: ; internal
09:11:04.250 [CM504003]: Sent registration request for 11111@BBTel
09:11:04.140 IP(s) added:[192.168.1.103]
09:11:02.531 *** Connected to albert:5482/CallManager at 127.0.0.1:5482 ***
09:11:02.218 [CM112000] Media Server is connected
09:10:59.015 [CM504007]: Next attempt to register 11111@BBTel is scheduled in 10 minutes
09:10:59.015 [CM504005]: Registration failed for: 11111@BBTel; Cause: 503 SERVICE UNAVAILABLE; from IP:200.112.128.83:5061
09:10:58.968 [CM504003]: Sent registration request for 11111@BBTel
09:10:57.406 [CM506002]: Resolved SIP external IP:port (190.16.209.190:5061) on Transport 192.168.1.103:5061
09:10:57.171 [CM506001]: STUN request to resolve SIP external IP:port mapping is sent to STUN server 75.101.138.128:3478 over Transport 192.168.1.103:5061
09:10:54.234 [CM501006]: Default Local IP address: [192.168.1.103]
09:10:54.062 [CM501007]: *** Started Calls Controller thread ***
09:10:54.062 [CM501002]: Version: 7.0.4708.0
09:10:54.062 [CM501001]: Start 3CX PhoneSystem Call Manager
09:10:53.500 Unknown system [DBProvider] tries to connect!
09:10:53.500 [CM501010]: License Info: Load Failed
Espero que sirva como referencia.