Sometimes cell phone reception varies by company. Not all towers are
compatible with the two common systems, GSM or CDMA. When a friend
comes to visit ask them what carrier they use and see if they get a
signal. Try several as some phones are more sensitive than others.
Another avenue is an antenna, some phones accept external antennas while
others do not. Check the Wilson Antenna site for your phone.
A third and more expensive route is a cell phone extender. It is like a
small repeater in your home for around $250. Again you have to find the
carrier with the strongest signal in your area.