I was having issues with constant dropped calls from my house, which is in an area according to the Sprint coverage map that should have excellent coverage. I went to my Sprint store, which is a repair center, and they told me to go to menu>settings>Wireless controls>Mobile network settings>Roaming, and switch from Automatic to Sprint only. I did this, and have not dropped a call yet. The tech told me that depending on exactly where you are and where the nearest Sprint tower is compared to the nearest say Verizon tower, the phone will continuously try to switch between the two towers for the best signal when set to Automatic, and that can cause dropped calls, static calls etc. Ever since I switched this setting I have not dropped one single call or gotten any static, even with 0-1 bars for signal strength. He told me only use Automatic if you are in an area where your phone has no service due to no nearby Sprint tower.
Hope this helps some of you that drop calls.