BillConner wrote on May 8^th, 2013 at 12:07pm:

... I'll stick with the Spot 2 three messages ...

With a little imagination and some preplanning, you could send a nearly infinite number of different preprogrammed messages using the two non-SOS Spot-2 buttons. For example:
   "I'm OK" = I'm OK
   "Custom" = I decided to delay my schedule
   Two consecutive "I'm OK"s = I'm really ok, even though I haven't moved in 5 days
   Two consecutive "Custom"s = I'm OK for now, but please keep checking email regularly in case things change
   Three consecutive "Custom"s = Not urgent, but please send outfitter to get me
   etc

You could even send morse code messages using the two buttons, but at about an hour per letter (a dot or a dash every 20 minutes), this is unlikely to be practical for most people.

For either of these approaches, you would also need some confidence in Spot's message sending reliability. My unit has been 100% reliable (so far), but I know others have had issues, and things like geography (eg high latitudes) and topography (eg Utah slot canyons) can interfere with the signal of even a perfectly functioning unit.