Contract Amount, Total Billed, Remaining contract amount

In the Accounts Receivable Module, having the option to track the total contract amount or purchase order approved amount, less total billed over the period or under the purchase order number, and the remaining balance on the face of the invoice or customer statement. This would require adding a budgeted or approved billing amount field, a field to track the amount billed, and the remaining on the face of the customer statement.