As far as I can tell, basic compatibility among STU-IIIs calls for the 2400 bps LPC-10 coder as a minimum. So it's universal. It works, but it sounds pretty bad, so there's been a lot of work on newer and better vocoders. Correct me if I'm wrong, but I suspect the Motorola coder you mention is probably one of several manufacturer-specific algorithms, sort of like the manufacturer-specific high speed modes you find on some fax machines. FED-STD-1016 CELP (Codebook Excited Linear Prediction) at 4800 bps seems to be the up-and-coming standard for newer phones, and it indeed does provide *much* better voice quality than LPC-10. Unfortunately, it also requires many more DSP cycles. Phil