Not sure why you think that pointing out possible problems with an idea means shooting it down. If the idea was bad then of course it does (and then it is well deserved), but if your opinion is right then it'll improve and hopefully we'll have it all in our pockets one day.
Here are my numbers:
As far as I know, an Iridium Phone ("be heard no matter where, no matter what") costs at least $1,000. So, the question is - how often would people use it? Let's say that a call costs $1,000. I have to admit that I have never been in a situation where I would have wanted to make a phone call for $1,000. So even if I'm greatly optimistic and 10% of all users ever make this phone call, then the price tag for the call would suddenly rise to $10,000. What you get is a vicious circle and at the end the company will need a few desperate millionaires who can afford to pay $10M for an emergency call.
Imho, the rich part of the world is just too safe for this to pay off, and the unsafe part of the world is just too poor to be able to afford it.