A signal processing system which discriminates between voice signals and data signals modulated by a voiceband carrier. The signal processing system includes a voice exchange, a data exchange and a call discriminator. The voice exchange is capable of exchanging voice signals between a circuit switched network and a packet based network. The signal processing system also includes a data exchange capable of exchanging data signals modulated by a voiceband carrier on the circuit switched network with unmodulated data signal packets on the packet based network. The data exchange is performed by demodulating data signals from the circuit switched network for transmission on the packet based network, and re-modulating data signal packets from the packet based network for transmission on the circuit switched network. The call discriminator is used to selectively enable the voice exchange and data exchange.