Jim wrote:

My guess would be all non-voice mode communications taking place in
the frequency coverage. I guess my main concern is what if I can't
receive even the voice communication unless it is FM or AM. For
instance, to hear trunk services, one needs expensive scanner (eg.
Radio Shack Pro-96). Any comments?

You can certainly receive non-voice comms with the appropriate
adaptor/decoder hardware/software. I have been copying packet for years.
I think many folks are monitoring ACARS, and probably many other modes.

Most, but not-all scanners cannot handle SSB voice.

Depends what you want to listen to - decide that and then select a
scanner with those capabilities. For me military aviation is a major
interest so AM between 118-150MHz and 225-400MHz is a must. I generally
am not interested in low band or anything above 512 MHz so I don't mind
if they are missing.

Dave