A technique for allowing a non-SIP user to call a SIP user includes dialing an established service number that indicates a desire to place a call to a SIP user. The SIP URI of the intended call recipient is included in a call setup protocol message associated with dialing the service number. A non-SIP network recognizes the call to the service number and the SIP URI from the UUI parameter of the call setup message. The call is then routed to a gateway for interfacing between the non-SIP network and the appropriate SIP network where the SIP URI is extracted from the message received by the gateway and used to generate an SIP INVITE message for establishing the call with the intended SIP user.