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

[Leo Burd]

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...