My gal is in a remote area as well, as far as cell signals go.
There can be differences in the phone's reception, even if the antenna is the same inside. The
type of signal does make a difference and some types reach further than others. Using a phone which covers more/all the variances of available carrier signals and frequencies will increase the odds of picking up a good connection. I got my sweetie a Samsung M8800 Pixon (not available in the US, got it there), and we never have trouble talking when she's at home.
However, before I got her that phone, she switched to a different network. At first I would have to dial 10-20 times to get through, and get disconnected after regular intervals (some days it was every 12 minutes, some days it was every 47 minutes, some days it was every 5 minutes). When she switched, my phone bill went down and our talk time went up. If she hasn't already, have her try sim cards from each of the carriers in her area to see which, if any, provides a better signal at home. The provider choice
can be the biggest factor in this. A better phone
can also make a notable difference.
I hope the issue can be resolved by one of these methods, good luck!
Disclaimer: I am not a wireless communications engineer, but I've worked with them before, and I am smart

Some of my terminology may be a bit off as well.