The effects of crosstalk on unsynchronized FDM communication links operating in the presence of additive white Gaussian noise are considered for several modulation schemes. Continuous-phase frequency shift keying is found to be far superior to various forms of phase shift keying in the sense that many more uncoordinated frequency division multiplexed waveforms can be packed into a given bandwidth for a certain imbalance in transmitter powers. This result can be applied to the uplinks and/or downlinks of a demodulating communications satellite serving a multitude of mobile terminals.