Why does my iPhone always say No SIM Installed?

At least 10 times a day, my iPhone service stops working and a message pops up that says "No SIM Installed". The only thing that gets the network going again is to restart my phone. It's an iPhone 5 and I've only had it since December. No drops, no damage. It's a minor defect, but it still really bugs me. What should I do?
Thanks.

As a matter of fact, it did it again while I was trying to post this question.

If I were you I'd remove the SIM to see if it stops poping up
if it stops then it must be something wrong with the SIM like its not placed well or its been damaged somehow.

If you have extra SIM card, try to replace it with the previous one. If the problem remains. Then may be there are two reasons: you are in a remote area so you only get weak cellphone signal or you iPhone is broken.