IIRC, it changed from 3 DTMF characters to 4 in the late 1990s. My Yaesu FT-50RD would decode DTMF and it didn't take long to figure out that it was just the station number followed by 1 or 2 # signs (1 before they changed, two after). WAY shorter than the state-of-the-art-in-1972 "pager" tones used by a certain city south of OKC, especially if you are dispatching more than a station or two. At least OKC never did it on the main fire channel. :roll:
For a while at least, on the EDACS system, they were doing basically the same thing but using i-Calls. At one point I had the numbers programmed into one of my scanners (as Unit IDs) and though the voice was digital, the station number would show on the display. Dunno if they still do that. Should probably check. Especially since I have the PRV key in my 436.
Along those lines, even with the PRV and DMR keys, a BCD996P2 is still cheaper than a BCD536HP without the keys.