I have had an iridium 9500 and 9555 for 3 years running the northern lights package.
I also have experience with the Globalstar phones...........and the dreaded inability to make calls.
My iridiums have worked flawless in all the mountain areas of northern BC. I have only ever had a couple dropped calls and every time I have been able to redial again immediately after.
In my experiences, situations and locations I would never venture into the backcountry with any other Sat phone. When my life or the life of others around me potentially might depend on it, I want it to work first time everytime.
Also if you disregard the initially higher cost for the iridium phone, the airtime is very reasonable, and the minutes roll over which is a plus.
As a side note I have converted a few friends over to iridium from other systems, soley based on the fact that mine worked when theres didn't. Same day, same location, same time............I was talking they where wandering around trying to get a signal........ hard to argue those situations.
just my personal experiences