A method is provided for determining origin ZIP code for a postage meter. The method includes receiving at a data center a call that originates from the location of the postage meter. Using caller ID, the data center determines the phone number originating the call. The data center also determines the identification of the postage meter. If the phone number has changed from a phone number from the previous phone call for the postage meter, the data center obtains a five-digit ZIP code for the address corresponding to the phone number. If the five-digit ZIP code has changed from a previous ZIP code used for postal accounting during previous transactions for the postage meter, the data center obtains a new certificate based on the five-digit ZIP code and downloads the new certificate to the postage meter. The data center transfers postage meter register values to a new postal account for the new certificate.