The problem is, this isn't how everyone operates. In Middlesex County anyway, I've only encountered DTMF for calling on JEMS 2, and the PL stays the same (103.5 Hz).
All my ambulances have PLs on Transmit, but none on recieve. It just makes it easier for anyone to call into the hospitals. We also have the DTMF encoders along with the list of codes for all NJ hospitals.