The empeg aux-in is normally used for audio FROM the handset to the speakers. In the other direction, I suppose the empeg MIC could be used, sampled, and fed over the serial link.

Wireline telephone uses 56kbits/sec (or 64 kbits/sec, depending on the system) for speech, so the serial link does have enough bandwidth at 115kbits/sec normal speed.

This would be fun to do -- maybe somebody with sufficient interest will have time in the upcoming recession to hack away at it!

Cheers