Can't make or receive a phone call n can't stop calling

Yesterday my iPhone4 suddently got problem. When I tried to make a phone call it showed" calling mobile" but nothing happened. I tried to end the call it showed" calling ending " then lasted forever, I turned to home screen then came back, it happened again and again.The only way I could temporarily get out of this situation was turning off the phone but it didn't help dealing with this problem because it repeated when I tried to do it again. I called my friendf by another phone and they asked me why they couldn't contact me n why I didn't say anything when I called them.

Moreover when I removed the SIM card, it showed " No service" instead of "No Sim " like before. I tried to turned on the "Show My Caller ID" following an instruction I have read but it kept loading so I couldn't do anything.

Anyone got the same situation and did figure it out, please give me some advice. Thanks a lot.