Abstract: System and method for extending the use of a VAT telephony application to originate calls into a PSTN as well as a computer network are disclosed. In a preferred embodiment, an adjunct application, referred to as a VAT signaling program ("VSP") running on the same host computer as a conventional VAT-based telephony application prompts a user to enter a destination telephone number and uses the entered number to generate a Q.931 SETUP message, which is encapsulated in a nonstandard, undefined, VAT control message (the "VAT Q.931 message") created to enable additional signaling information to be sent. A signaling interface to the PSTN serving the designated telephone number signals to the VAT application software exactly as if the signaling interface were actually another VAT application software originating a call to the naive VAT application. The signaling interface waits until the user at the computer "answers," and then originates the call into the PSTN network.