Processing telephone number

Hi,

I have an openldap that stores information of my users. One of the fields we are using is telephoneNumber to store the phone number of the user.

In this field we are storing now the complete phone number, that is, a number like +34 123456789, but now we are deploying applications that need just the extension number (the last 4 digits), not the hole one.

Is there any overlay or other option we can use to provide those last 4 digits of the telephoneNumber attribute without needing to store them in another different attribute?