I travel every weekend between Big Bear Lake and Palm Springs down Highway 18 to 247.  There are at least four spots where my iPhone7 plus with Verizon service dropped calls like clock work in the past.  Since installing this (took ten minutes), no more drops. I've found it increases my signal strength by a bar, probably just enough not to drop the calls in those areas with on the edge reception. I'm going to get another for my truck.