Entirely unhelpfully, the Smart 500 on the 738 is as follows:
Smart 500 Radio Altitude Callout
The Smart 500 Callout annunciates FIVE HUNDRED during a non-ILS or
non-GLS approach. Activation of this callout is dependent only on lack of an ILS
or GLS. However, if flying an ILS or GLS approach, and there is excessive flight
path deviation, the GPWS will conclude a non-ILS or non-GLS approach is being
flown. This feature functions with or without any of the normal altitude callouts.
When descending below 500 feet radio altitude on approach, a FIVE HUNDRED
callout is given if:
• an approach other than ILS (the ILS frequency is not tuned) or GLS is
used, or
• a backcourse approach is detected, or
• Glideslope Cancel is selected, or
• the flight path is not within +/- 2 dots of a valid localizer beam (excessive
ILS or GLS flightpath deviation), or
• the flight path is not within +/- 2 dots of a valid glideslope (excessive ILS
or GLS flightpath deviation)
Given it comes from the EGPWS, I assume it works based on the software in there, which would probably be the same version across different types depending on different operator options and specs.