An in-vehicle system (IVS) captures data such as location data and in an emergency automatically places a call to an emergency call taker or PSAP via a wireless telecommunications network. After a voice call session is established, the IVS system transmits a predetermined control signal through the voice channel. The control signal directs the call taker system to prepare to receive data. Preferably, the control signal comprises at least one audio frequency tone. This may be done without human intervention. In this way, emergency information is transmitted accurately and with minimum delay. After transmission of essential information, the IVS system may switch on audio connections for live human voice conversation.