Hams have used 1200Bd AFSK FM as the physical layer of AX.25 for decades, though with variable implementation quality.
Whilst the AX.25 packet networks of yore have all but died, the protocol is currently used with APRS, and so the related issues remain relevant… well as relevant as APRS remains. Continue reading AX.25 1200Bd AFSK FM – to pre-emphasise or not