[Is there a way, yet, to purge a voicemail box of existing messages?]

Maybe a manager role with access to user portals and end user settings

[Call recording to Google Drive storage?]

Why can't you just add a column inside of monster for recordings and just SYMLINK it to an Amazon storage! It is very inexpensive "LIKE 0.03 PER GIG" and you don't have to worry about using up the storage on the local PBX. Admins, Resellers, and even Customers could add their AWS API key/token what have you and instantly connect!!!

[Is there a way, yet, to purge a voicemail box of existing messages?]

It would be nice to masquerade inside of user accounts , a lot of my customers don't even use the user portal so I have to set a temporary password login and help delete their voicemail messages...