no simm error on 4si

I was using my phone as a GPS yesterday, stopped at store unplugged headphones, when returned to car had error no sim card. showed no sim on screen for signal bars. could not get it to work for about 3 hrs. even after turning off and back on 3-4 times. then after trying again it started working. is this something i need to send it in for service on? phone is about 1 week old.