I made the experience that older cell phones have way better reception than smart phones, when it comes to plein talking connection in areas with poor coverage.
Many times, from top of the mountain when you even could see the antenna far down in the distance, the local guy would be chatting away happily with his old Nokia, while my brand-new smartphone kept searching for connections, just to finally refuse to book into any on the list of available nets (be they 2G or 3G).
I never would describe any call phone as a safety device, but just as a "nice to have" item. Always be prepared that it will fail when you really need it.