Manage minutes on a Sip trunk

Is there a solution for defining a # value for minutes that a SIP TRUNK will
So i would like to have my sip trunks do lets say 300 minutes per trunk
(a pre defined value)
The system outbound should randomly pick sip trunks regardless of their order.
If all has reached their limit 503 congestion takes place.
Any ideas?

Search this site for load balancing trunks and you will find something that might help