Based on the TI data sheet, it should work at almost any speed as it doesn't time the frequency shifts, it just responds to them as they happen. It is only an FSK modulator and demodulator, it doesn't care what speed you feed to it but obviously there is a limit determined by the number of cycles per bit in the audio waveform. The data sheet shows configuration examples for 600/600 and for 150/150 Bauds. You should keep to the same crystal frequency though as it determines the filtering characteristics and tones.
Brian.