billing software to manage our billing

Hi. I am looking for billing software to manage our billing. The software we are looking for would have most, if not all, of the following requirements: *Multi-user. *Multi-vendor to allow for different billing strategies and access - each business interest may have their own customer base. Each business interest may have their own view of the system. *Flexible in bill style/format and fields printed on the bill. *Ability to print bills ordered by zip code. It would be nice to sub-sort by either alphabetical or account number. *Flexible database view - we can customize the view into the database based on the buseinss interest. *General purpose report generation. *Billing cycle flexibility based on the buseinss interest. *Maximum billing amounts - we may select taht the computer not bill on amounts great than, say, $3.00. This is business interest specific. Can anyone point us at products that provide these kinds of capabilities? Thanks, Stew