We all have a good idea about what an extension is. On our legacy PBX, each handset was an extension. Pretty simple, right?
While conceptually simple, there is a little wrinkle. If all we want to do is provide a few handsets, then there's one extension per phone. But Asterisk can do much more! We need to think of an extension as a group of commands that tells Asterisk to do some things. As amorphous as that may be, it's true.
An extension can be tied to one handset, a queue, groups of handsets, or voicemail. An extension can be attributed to many different areas of the system. If you're familiar with programming terms, perhaps you could say that extensions are polymorphic.
To go further, extensions can be used to provide access to other applications, sound files, or other services of Asterisk. Extensions are important to the magic of Asterisk.
Now that we know why we create extensions, let's think about how we create them. Again, they are in the extensions.conf file, or...