UPDATE
The nanoShout
http://www.satellitephonestore.com/nal-nano-shoutIs another small 2 way messaging system, one that does not need a smart phone to work.

Pretty cool tech, eh?
Also, now on the market is the GeoPro messenger
The affordable, rugged GeoPro Messenger device supports global two-way text messaging. Along with hassle-free check-ins, the GeoPro Messenger also makes it easy to call for help in an emergency and provide in-event updates to assist first responders.

And the Iridium Extreme messages and two way voice....wow.

Ruggedly engineered satellite phone, personal tracker and SOS device
Covered SOS/emergency button
User selectable tracking interval
LEDs for SOS and GPS
Easy to use in one hand with non-slip form factor
Global coverage everywhere over the Iridium network
Vendor site
http://www.geoprosolutions.com/devices/Lot more choices out there, and the prices have come down. Once the Army pulls our of SWA, the satcom folks are going to be scrambling for customers. Hopefully the price will reflect the desire for new customers with less-than-deep pockets.