That's not good. Have you tried resetting network settings? By doing this you may have to reconnect your wifi connections but it may help. Or you could visit a corporate store and have your SIM care replaced.
I have an iPhone5c. Cell service has been fine since I opened this account on April 24th, 2015. I tried to power off and on. I reset my network settings. I still can only receive calls, send and receive texts but cannot make outgoing calls. Why?