Since the No SIM problem is commonly caused by a dislodged SIM, try reseating it. After a few seconds (up to a minute), the No SIM Card Installed error should disappear and your bars and carrier name should reappear.
If your iPhone still doesn't recognize the SIM, try the all-purpose fix for many iPhone problems: a restart. You'd be surprised how many issues are solved by restarting.
If you're still seeing the SIM error, your next step is to turn Airplane Mode on and then off again. Doing this can reset the iPhone's connection to cellular networks and may resolve the problem.
Your phone account may be invalid. You need an active phone company account to connect your phone to a network. SIM error appears if your account is suspended, cancelled, or has another problem.