Samsung Gem phone troubles?

My wife has a samsung gem smart phone and for the past couple of months, she's been having trouble with it. her provider is Alltel and most of the time, she can't use her phone due to loss of service. she just got a replacement phone, same thing, and its again...the same troubles. i know her phone is 'roaming' cause of our area, but as far as apps and whatever else, she has very little on it. We both dont know whats the deal, and Alltel seems to be stumped too. Any ideas? Thanks!!