Abstract: A computer-aided billing system which directs the printing of customer invoices to include current billing information and transmittal charges for a pre-paid return envelope which the debtor will receive with the invoice for use in return of the invoice payment and which also directs collation or assembly of the pre-paid return envelope, the invoice, and the shipping envelope in which the invoice and pre-paid return envelope will be sent to the debtor. The computer-aided billing system contemplates debtor agreement to pay the transmittal charges and the possibility of future transmittal charges for electronic transmittal of invoices and invoice payments. Applications include, but are not limited to, use by banking institutions and credit card companies.