Q: after update 'no sim' shows up on the screen

I have recently updated my iphone 4 with the new operating system and suddenly "no sim' has appeard on the top left corner of my screen.  I re inserted my sim.  I restarted the phone. I followed the troubleshooting advice and attempted to restore my phone but towards the end of the process it needs to activate the sim and it can't.  I have tried to send a query to apple but I have to send my IMEI number and I can't get to it because my phone does not work ( due to the sim not being recognisedn- has this happened to anyone else? Any suggestios???