Abstract: A method of using accounting certificates to allow a subscriber of a home network to purchase services or products via a mobile communications network, the method comprising sending a request for an accounting certificate from a subscriber's mobile terminal to a certificate issuing node, upon receipt of the request at said node, sending an authorisation request from said node to an online charging system of the subscriber's home network, at the online charging system, making a decision on said request based upon the subscriber's account data, and returning either an accept or deny service request message to said node, in the event that an accept service request message is received by said node, sending the requested accounting certificate to the subscriber terminal, and sending the accounting certificate from the subscriber terminal to the provider of a product or service to be paid for.