Where we are for the summer, we are on the fringe of cellular coverage and are lucky to get one bar. So, we got a Wilson dual-band amplifier and external antenna. It raised our signal strength to the point that Magic Jack, our cell phones, and Verizon Mifi air-card all work well (3 to 4 bars). We bought a mobile system so that we can move it to the TV while on the road. I love to have the DW doing her thing on face-book so that she doesn't "help" me drive.
The system has 2 internal antennas. One has a capability to hold my phone (or air card) on the dash board. Allowing good blue-tooth connection to my radio (or good signal strength for the computer). The other antenna is a proximity antenna that we just hold the phone (or air card) close to. The system isn't perfect, but it solves our problems with connectivity.