I've been using AT&T phones on the Appalachian Trail since 2006. In 2006 both AT&T and Verizon seemed to have equal service on the trail. Since 2009 I've noticed the Verizon customers getting a signal in more places where I could not.
I never used the phone in the shelters as it is poor etiquette. I would walk away from the shelter to the highest place around it away from the ears of others. This not only kept the conversation private but also helped improve the signal strength. If I couldn’t get a signal near the shelter I would take out the phone during the day on some high point and try again.
Keep in mind the shelters are usually placed in valleys because that is where the water flows and many do not get a good cell phone signal. Make sure your wife is aware that you are in the mountains and may not have a good enough signal for days and she may not hear from every day. I understand a text message can be sent and received with a weaker signal than it takes for a voice conversation. You might be able to send a quick “I’m fine at ___ location” in places where the signal is weak.
A device I am seeing more and more is a SPOT locator. It is a little device that sends your location up to a satellite then sends a predetermined “I’m fine at ___ location” email or text message to people you set on a mailing list. They can then see your location on Google maps. The device has emergency features that can alert emergency responders of your problem and your location. Check out their web site at http://www.findmespot.com/en/ for features and cost of the service available.
I originally kept my phone in a ziplock bag until I got caught in a downpour and the inside of the bag got wet and killed the phone. I now use a small dry sack specifically made for small electronic devices.
Incidentally don’t rule out place along the trail as being too remote for a signal. I thought I would be in No Mans Land when I entered the 100 mile wilderness and was pleasantly surprised to make calls in a number of places.
_Old Goat_