A telephone interface to an Internet payment processing system. The interface may be installed on equipment used to process a card transactions. When a request for authorization is initiated, the interface dials a telephone number and establishes a connection to a communications server. The interface creates a message comprising the transaction data that conforms to the hypertext transport protocol (HTTP) and transmits it over the telephone line to the communications server. The communications server establishes a TCP/IP connection to a web server and the HTTP message is forwarded to the web server where transaction data is extracted from the HTTP message and formatted for submission to a card transaction processing network. The transaction is submitted and an authorization code approving or denying the request is returned from the network to the web server, to the communications server, and then to the merchant terminal using the telephone line.