What happens is they have their vm delivered to their email and left in their extension. They don't want to delete them through the phone and so far... no one likes the 3cx phone. Most of the users come from previous environments where they could just goto a web page, and delete the files themselves, so that is where the ask comes from.
When they complain enough I just login and delete the vm files for them, but many users and management have asked for this feature.