If you just want to add a zero in front your phone number called, then you must put a zero into your config trunk - Outbound Dial Prefix .
Freepbx contextual help:
The outbound dialing prefix is used to prefix a dialing string to all outbound calls placed on this trunk. For example, if this trunk is behind another PBX or is a Centrex line, then you would put 9 here to access an outbound line. Another common use is to prefix calls with 'w' on a POTS line that need time to obtain dial tone to avoid eating digits.
If you have one extension named 100 you can't dial 100 to do an outgoing call!
Generally, to do an outgoing call from extensions, you must use outbound route menu and add a new route with a good dial pattern, and putting your prefered trunk.
For example, in dial patterns, put "0." , that's all.
All phone numbers begining by 0 will take this route.
But be careful, the 0 will be sent too.
If you want to delete it, then use dial rules: 0|.
Before the pipe, the numbers are deleted.
Just read Freepbx menu.
If you see misc application, then it's this menu and not another.
Next, read the fields which you could set. You have only 4 fields: - Description:
- Feature Code:
- Feature Status: