To remove the SIM card from your iPhone, you'll need to eject the SIM card tray with a special tool or paperclip.

If you need to find out your iPhone's carrier without a SIM card installed, you can do so through the Settings app.

Turning your phone's connection off and then back on is the quickest and easiest way to try and fix your signal woes. If you're moving around from one location to another, toggling Airplane mode ...