For some reason I remember hearing or reading a long time ago that IFDs would behave identically and provide the same callouts whether the TAWS feature was purchased or not. I also asked an Avidyne employee about this recently at the Cirrus Migration expo and he said he was pretty sure I'd get the TAWS callouts even without the TAWS license.

I'm confused though, since the pilot guide seems to imply that I shouldn't get PDA, EDR, or NCR callouts from my non-TAWS IFD540. The root of all of this, is that my Cirrus was originally equipped with the Honeywell EGPWS system, which does provide these callouts. For the last year or so I've kept that system disabled, and enabled FLTA on my IFD so all of my callouts come from one piece of equipment.

Am I missing some capabilities by doing this?

I believe the TAWS option needs to be purchased / activated to get the PDA, EDR, and NCR callouts. All of the other FLTA and altitude callouts come standard with the F500 option.