Unfortunately, modern handset phones are all limited to .6 watts of transmitting power for safety concerns now (and older phones with greater transmitting power, aren't allowed to be connected anymore by law unless they were already connected prior to a certain date). This means, for the most part, every handset phone you buy today is going to be roughly equal in its ability to pick up a signal. Connections rely more on your carrier than on your phone.

That's not to say that there aren't other options. There are still companies that make bag-phones, which are allowed to transmit at greater power levels. Unfortunately they are expensive and difficult to find. Then you've got satellite phones that are even more expensive, but will get a signal just about anywhere as long as you can get a fairly clear line of sight to the sky.

Personally, I've got GM's On-Star in my truck, which works on the same network as cell phones, but uses a significantly more powerful transmitter (3 watts). Typically I can get a signal with that when I can't get one with my cell phone. The downside though, is that it's built into my vehicle.