TAG.
I spend a bit of time in the backcountry myself and looked into both the spot and delorom options, but man are they pricey for someone who only uses them a few times per season.
I went with the above posters open, both an AT&T and Verizon phone when in the backcountry. Opens up your opens vs only having one carrier.
Verizon and AT&T work of different towers because they operate using different technology.
GSM & CDMA. A quick but not really correct way to describe it to those who have no interest in detailed technological explanation is FM or AM radio.
My primary phone is an AT&T smart phone, but I also keep a Verizon prepaid plan for those times when I am in the backcountry and only have service from one or another, or god forbid a realistic disaster scenario taxing the phone system.
I also carry a VHF/UHF hand held radio, being a ham, and working in the communications field, I have knowledge and the ability to utilize many radio repeaters in and around my AO. Not an option for most but figured I would throw it out there.
With all that said, even the two cell and ham radio option is not a sat phone or sat emergency communicator, just other options.