[lgats]

didn’t have much luck with multiple baud rates and modulations on minimodem, no discernible ascii, but someone might have more luck looking at the binary output

[ajxs]

It wouldn't be encoded in a modem protocol. If that's indeed binary data, then most likely we're hearing binary data interpreted as being PCM wave data.

[jojobas]

That would almost certainly be damaged by phone line bandwidth and voice machine compression.