An operator reading a cluster page sees 28500 and wants to be there. The
hands are on the callsign field; reaching for the frequency box, or the
mouse, is the part that loses the station. So the call field takes a bare
number on Enter: kHz for a frequency, or a band on its own.
Ambiguity resolves to the band on purpose -- 40 is 40 m, not 40 kHz --
because neither of those kHz values is anywhere a radio tunes, and it
reads the way an operator says it. Anything with a letter in it is a
callsign and behaves exactly as before; a number that is neither a band
nor a plausible frequency does nothing at all.
Bands go through the ordinary band change, so the antennas, the per-band
power table and the outbound integrations hear about it as they would
from the dropdown. Also adds 4 m to the QSY table, so a band that can now
be typed is a band that has a frequency to go to.