After some research into their effectiveness, I elected to buy a booster/amplifier for the boat. We spend a lot of time on the water in the warmer months and I got tired of poor cell reception in the middle of Lake Michigan.
What a difference this thing has made. We have since installed them in every vehicle we own. No more dead spots or weak signals to date. Well worth the investment.
I bought the DA4000 dual band works with all verizon, at&t, pcs etc. They have another one for nextel. Made my own RG-58 cables.
I have no affiliation with this company, but I like their products:
http://www.digitalantenna.com/
Another company that sells a similar product, I have no experience with these products:
http://www.wilsonelectronics.com/