It is likely a common scenario that a client is on a monthly retainer for maintenance, so they do not pay extra for fixing problems, but if they want a change made, they get billed by the hour.

There is a way to change the ticket type - Problem/Change. so the ticket is categorized correctly- and a way to change the contract, so they can be billed appropriately, but it would be nice if the Ticket Type could be linked to a Contract so they are billed based on ticket type.