Alias to Extension number


how to add to Extension main number additional number as alias?

Can you make an example! Your requirement is still ambiguous.

For example:
we have extension with number 123.
now we need add alias to this extension (number 124).

What is the purpose of the alias?

That might help us steer you in the direction that will be the most efficient, since I can think of about 10 ways to do that without even getting tricky.