Warning System before getting close to PM limit?

[NameTower]

Maybe a message could popup when you have 5-10 spaces for PM's left.
wouldn't be too hard to implement, but would be pretty useful to some I think.
just a little javascript alert... or even just text on the page in bold or something

 

[VisualDigits]

I know what admins would say: upgrade to exclusive!

 

[GiantDomains]

When your PM box is full, you get an alert in your email "membername" tried to send you a PM but your box is full. So just delete some PMs, and PM the member.