Extensions are internal numbers that can be linked to actions. Extensions are unlimited, actually nothing more than a label and 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, the call 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 is an echo test if no answer. In this set up the call will never reach the echo test when the rule of an extension has ended, or if there was no applicable condition.
In order to reach the right effect, an Inbound rule should call a PBX user and on no answer go to the next rule.
Another approach is to add the echo test and then add a second rule in the rules list of the extension.
Try to define all rules in Inbound as it helps the readability and makes it easier after a period of time to still understand the call flow.
See Rule editor type list for a complete list of rules and possible conditions.
202 will be routed to PBX-user 202, followed by it’s voicemail.
1233 will 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 in order to facilitate 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).