Since billing is nearly always directly tied to the estimates created at the beginning of the job, usually you will want to pass on the estimate (or a summary of the relevant portions) to the person who is going to do the billing. This way, the person knowing the billing knows how much to bill. There are several ways to do this; which you choose is largely a matter of your preference:
Print summary pages from the estimate and give the paper copies to the accounting staff responsible for the billing: While this option requires paper and manual delivery, billing is fairly simple so some offices still prefer this method.
Send an email (journal) to the billing staff with the estimate document attached: Attaching the estimate to an email/journal eliminates the paper and manual delivery of materials. It also gives an easy way for the recipient to reply and indicate that the billing is done.
Create a folder for each month's billing and post each relevant estimate in that folder: For example, you might create a folder named June 2002 billing, another named July 2002 billing, and so on. Managers would then associate each estimate to be billed with that folder (either directly or through a journal entry). This eliminates paper handling and gives a concise view of everything submitted for billing for any month. Once the billing for the month is done, just make the folder inactive to remove it from view.