[development] How to call a function when a certain permission is set?

Hello there, Is there any way to call a specific function everytime a certain permission is set or reset? For instance, if the admin users allow users of a specific role to have access to voicemail, I'd like to create voicemail boxes for the users that already exist in the database. Not just for the new users that will be created over time. What do people do in a situation like that? Thanks in advance, Leo PS. I'm using Drupal 4.6...