Sometimes, the number is printed on the SIM card. First, you need to eject the SIM tray. Use a SIM ejector tool. This usually comes with your iPhone. If you don't have one, a paperclip works. Gently push the tool into the small hole. The tray will pop out. Carefully remove the SIM card. Look for a long number printed on it. It might be tiny. A magnifying glass can help. This number is... aolists.com