What's the difference between a GPS handheld and a satellite communicator?

A traditional GPS handheld (like the Garmin eTrex or GPSMAP button models) shows your position and navigation maps offline using satellite positioning, but does not let you message anyone. A satellite communicator (Garmin inReach, ZOLEO) adds two-way text messaging and an SOS button over satellite networks, which requires a paid subscription. Some units, like the GPSMAP 66i and 67i, combine both.