A method (60 or 70) and system of reducing collisions in an asynchronous communication system can include the steps at a transmitter (200) of generating (61) a set of known preamble waveforms and transmitting (64) at least one distinguishable preamble waveform based on an association with a call type and a receiver identifier. The method (70) can also include the steps at a receiver (300) of receiving (71) at least one preamble waveform among a set of different preamble waveforms which toggle between two symbol frequencies, the different preamble waveforms being distinguishable by at least having one among a different symbol frequency spacing and a different symbol toggling duty cycle. The method further includes the step of selecting (73) to decode a preamble waveform based on at least one among the different symbol frequency spacing and the different symbol toggling duty cycle.