This will be mostly used for non-routine calls, but for more than just emergencies.
For these circumstances in Alaska I've rented Iridium handsets with prepaid minutes. You'll have to shop around as providers' plans seem to change from season to season, but prepaid minutes are typically cheaper than by-the-duration-of-the-call plan. There are also plans that have free SMS and / or voice mail.
One problem with the prepaid minute route - it can take 10-15 minutes to 'recharge' your phone, so apply more time well in advance of your anticipated need.
The only reliability issue I've had is with a poor antenna connection; when attached to a fixed-mount antenna (coax feeder), the phone would occasionally reboot. I think something in the antenna collar was shorting out as the coax flexed, but I don't know. That happened only with one particular phone and I haven't heard of it happening to anybody else.
I haven't had a problem with coverage yet.