By changing the Dial Plan it is possible for the PBX to add the leading number indicating which SIP trunk is used.
For example, there are various ways to dial a regional number in Amsterdam using trunk 0:
00201234567 - in regional format
00031201234567 - in international format
01234567 - in local format
To use SIP trunk 1 for a call to a regional phone number in Amsterdam you enter the following on the phone:
Version 3.0 and above includes the 'default trunk' feature. It allows users to dial external phone numbers without the trunk number. Normally a user would dial 00201234567, when the feature is enabled the PBX will automatically choose trunk 0 when the user dials 0201234567.
If your Axeos PBX is an older version the automatic trunk selection may be possible by editing the Dial Plan.
Login to the PBX and go to menu option 'Dial Settings' and select 'Dial Plan'. Enter the following to the Dial Plan:
Note: The Dial Plan change only works if the SIP provider accepts numbers in national format. It is not possible to use these settings in combination with ISDN.