Our situation is that living in SoCal very close to the beach, we have practically no cell service. AT&T's cell tower coverage map indicates we have 3G, which I thought would be great having bought an iPhone a month ago. Well, I'm lucky to get "one bar", and if I walk from our
front door into the back of the house, in many cases I end up with the dreaded "no service" message.
Fortunately, Wi-Ex makes this neat product, called the "zBoost Cell Phone Signal Extender". We've been using it for over a week and it works! We now have consistently 3-4 bars thru-out our house, and there's no need to conduct phone conversations sitting on the front steps by the street - in your bathrobe!
Highly Recommended
(Photo and blog post from my iPhone)