Professionally, in the recent past I have used both Globalstar and Iridium sat phones. To the best of my knowledge those are the only two companies providing sat service. As stated they work well provided there's a clear view of the sky and the battery is well charged. When I first had one it required a view of the southern sky. For me that has only been a problem in the extreme north latitudes, and I guess extreme south latitudes, and steep terrain. I suppose with the passage of time that maybe now there's a commercial comm satellite on a polar as opposed to just equatorial orbit, thus eliminating that requirement. I've had signal interference from both terrain and tree cover requiring me to move around, sometimes a long way till getting a signal. The Globalstar always seemed to get a better signal when attached to the external antenna and the hands free, (Vehicle) kit. Frankly we've scaled back on the sat phones and have found that using power boosters, (NOT those sold on late night TV) and external antenna's with our cell phones meets the majority of our needs at less cost. The down side of course is the booster is wired to the truck, (no truck=no booster). For those times I work really remote I do have an Iridium available and carry two batteries. It works well, seems rugged enough, though sometimes I still have to climb a hill to find the "Phone Booth". In my professional case the phone is more to facilitate business than safety as we have a stellar check in/check out system and I personally abdicate that all travelers develop one. There was an issue with blockage to satellites, I don't remember if it's still an issue or an issue specific to a given vendor. When at work tomorrow I'll check with comm geek #1 and can confirm if satellites are still an issue and post an update.
I personally think the PLB's have merit but my only experience with them are avalanche beacons. Fortunately I've never been caught in an avalanche and forced to use mine.
