You will receive the following information from Atlantic Telecom:
The SIP URL shows the hostname and the username in the following format: username@hostname.
Login to the Axeos PBX, go to menu options 'Dial Settings' and choose 'Outbound'. Create a new outbound trunk.
Complete the settings using the credentials you have received as shown on the screenshots below (including the Realm field).
Screenshots
Once your outbound SIP trunk has been created, you can enter your inbound number at 'Dial Settings / Inbound' using the following number format: 31201234567
NOTE: if you can not receive incomming calls add an inbound 's' number to enable call routing, as shown below: