Extensions are internal numbers that can be linked to actions. Extensions are unlimited and are nothing more than a label. Extensions can be part of a call flow.
A strong word of advice: do not create extensions in the 1XX range as this conflicts with e.g. the 112 European emergency number.
Caveat: once a call starts with rules of an extension it will never return to a calling rule in the inbound dial plan.
Example: An external call starts with the rules in Dial Plan/Inbound, the first action is to dial an extension. The second action an echo test if no answer. In this set up it will never reach the echo test when the rules of an extensions has ended or there was no applicable condition. To reach that effect then the Inbound rules either call a PBX user as rule and then on no answer go to the next rule. An other approach is to add the echo test then add a second rule in the rules list of the extension. The preference is to define all rules in inbound as it helps the readability and makes it easier after 6 months to understand the call flow.
See Rule editor type list for complete list of rules and possible conditions.
Overview of extensions:
302 can be routed to PBX user 302 followed by its voicemail
1233 can be routed to the Voicemail Menu.
Extensions/phones often have three digits, the European alarm number 112 needs to be included as an extension and linked to the ‘Call an external number’ action.
06302 can be routed to the mobile phone number of user 302 to create short number dialing functionality.
You can add multiple rules to an extension. Each rule can be applied based on a condition (status / callerID / time rule).