IAX Username and extension

I am new to this and would like to know what the generally used solution is to usernames an extensions, what I am trying to say is when i setup accounts for IAX clients their username is the same as there extension stored in the []
. I want to use numbers as extensions for pattern matching so I dont have to input everyones number extension and then dial command.

I dont want users to loging for example as username 1002 but instead use their name as the username to login with the IAX client , but i want their extension to be 1002 so i can DIAL(IAX2/1002) and then use pattern matching to cover all numeric extensions

I hope this makes sense