Many times support techs forget when and when not to bill an activity. This could translate to a lot of lost revenue and we don't really have a review screen.
Under inquiry contract usage, add a tab for all activities (or non billable activities). Provide a selection box to on the fly move these items to unbilled tab so that they can be billed. Many times accounting or services does a spot check to ensure everything that needs to get billed, gets billed, this would be very helpful.
Another idea is to add an activity tab to Contracts. We have it in Project, we should have it in contracts. And allow selection for making an activity billable. Be sure to enforce that any one activity cannot be billable, if it has already been billed.