It would be really useful to be able to create an invoice for pre-paid support hours.
A client pays for 10 hours of support a month at a fixed rate. This put 10 hours "in the bank" for them.
Then any ticket time or other logged time is marked against these hours. And additional hours are billed at the set client rate.
This would allow a preferential rate if there is a regular support hours contract, or if a client wanted to pre-purchase a bulk number of hours of support.
Ideally there would be the option for hours to roll over or expire.
EXAMPLE 1 - a client purchases 10 hours a month, they expire at the end of that month,
EXAMPLE 2 - a client purchases 20 hours of support, to be used as required without expiry.