I have the original Spot plb/messenger device. Works fine, though I havent used the tracking much and it is seeming like an expensive luxury. With the price of everyday plb coming down all the time i'm thinking these are not the best value.
Seems to me we are pretty much drip fed satellite technology. Narrow bandwidth aside, i cant see why a gps enabled smartphone cant just also operate its communication permanently on the satellite network without huge added expense (different networks perhaps? (i'm no techead..))
Anyhow... For those with a smartphone, you can at least access the Spot network and at least send SMS now. I guess if you carry the phone this would be a bit more convenient and a way to get plb backup anywhere perhaps (or course there is the obligatory $100+ per year):
http://www.findmespot.com/en/index.php?cid=116