Provide a field for POs in Project setup
Add tracking info to the Projects setup.
Provide a field to for a PO# when creating a new Project. The Invoice template should retrieve the field name and value when we're billing for the project. The Project list/report should also display the PO.
A field for a Job Number or Docket would also help.
Anyone working freelance as a copywriter, graphic designer, web developer, etc, would be accustomed to using these features for timesheets and for billing.