Need to write a simple form with
customer name ,
and mailbox Yes/No
then send info to an Asterisk /Elastix server to create an extension with the information and incoming for that DID to go to the extension.
the information could be send with a query or via curl with a hash key on both sides.
You will be given access to a web server as well as the Elastix/Asterisk server for testing, the Elastix server is not on production.