There are not many more than four things that could make your phone not work. If there is a problem with the carrier's network, they should be able to tell you. If the phone is defective, you will probably need to get it replaced by the store you purchased it from. This is called crosstalk. It is the result of a strong signal from one phone crashing into another phone's weaker signal.
Crosstalk usually fades away after a moment or two.
Hanging up and connecting with your party sometimes connects you to a wireless tower, which will increase your signal strength. Wireless uses line of sight transmission. Often, forest preserves or large hills will block transmissions. Wireless carriers continually tweak and adjust their systems to minimize these areas. Some authorized dealers handle phone repair.