No Simcard installed - iPhone 5 I've got an iPhone 5 running the latest iOS 7 version. (I don't feel like testing the first pre-released iOS 8).
The iPhone randomly displays me "No sim card installed" in a pop-up and I have no provider in the left-top of the menu.

What have I tried:


Toggling AirPlane mode (this does not work)
Hard reset (this works)
Removing the sim card using a paperclip and placing it back (this also works)


What I didn't try:


Restoring the device I don't see why restoring my iPhone would solve this problem.

What can cause this issue? 
I'm still under warranty by the European law (which is 24 months for an iPhone)
This is often caused (but by no means is this the only possible cause) by a badly fitting sim card, or sim tray.  That doesn't explain how a hard reset would make it work though.  I would see if you can borrow a friendly sim and tray from another iPhone 5 users, and see if you can get the same results, or improved results, by using different combinations of sim card and tray.  When you get one that works, run away and leave your friend with the duff bits ;)