well if you want to drop about $150 you can do what i did and get a wi-ex wireless extender.
http://www.wi-ex.com/Page3427.aspx
no wires to plug in to your phone at all. it has 2 antennas 1 for out side 1 for inside it repeats the cell signal. with it the 3 sprint phones in my building went form 1 bar to 4-5. They only work with 2 phones at once. So if 3 or more people try to call out or in at the same time you will see some lost calls. But other then that they rock.