K2DLZ: "It is my understanding that SSTV is a data mode and CW is a digital mode. So only those data / digital modes are allowed in the phone bands."
SSTV is an image mode. That's where FCC draws the line.
K2DLZ: "CW takes about 800 Hrtz while pSK takes 31....?"
CW takes a lot less than 800 Hz! The actual bandwidth depends on the keying waveform, but 100-200 Hz is more like it.
K2DLZ: "Seems to me that PSK should be allowed in the phone bands and CW / SSTV not! (yes I know SSTV ops need to use ssb for discussion purposes after each pic)...."
AN SSTV signal is about the same bandwidth as an SSB signal, too. An 850 Hz shift RTTY signal is much wider than a CW signal, yet RTTY isn't allowed in the 'phone subbands.
It makes sense to keep narrow signals with narrow signals and wide signals with wide signals. But it's not Just about the bandwidth of the signal. It's about the kind of signal. Why the kind of signal matters, I don't know.
Looking at the history (in the USA), here's what I see:
Decades ago, the only modes allowed were CW and AM voice. CW was allowed everywhere but AM was restricted on HF to a few parts of a few bands, because it took up so much spectrum and hams had so few bands. CW was allowed in the 'phone subbands because that way all hams could communicate with each other - at least in theory. Also, if conditions changed so that 'phone couldn't get through, CW could be used to finish the QSO.
After WW2, modes such as NBFM and SSB became popular with hams, and the logical place to put them was in the 'phone subbands. The 'phone subbands were expanded, and we got more bands (15 meters in the early 1950s, 30, 17 and 12 in the early 1980s).
RTTY, OTOH, was put in with CW. For many years, the only kind of RTTY allowed to US hams was 5 level Baudot RTTY at 60 wpm (45.45 baud).
When SSTV came along in the late 1950s, it was put in with 'phone because it took up so much bandwidth, and because SSTV was usually implemented on a 'phone transmitter.
Also, except for SSB, when those new modes showed up they were originally limited to small parts of the various subbands. Over time, that was expanded.
Since the early 1980s we've gotten a lot of new modes, many of which are implemented by PCs. FC loosened up the rules, treating AMTOR, PACTOR, PSK31, MFSK and others as simply new forms of RTTY, the same way they treated SSB as a new form of AM. At the same time, they widened the 'phone subbands, which squeezes those operations into less and less HF space.
Maybe it's time for a rules change?
73 de Jim, N2EY