When purchased, iPhones come with this pin that you use to open the slot on the side to insert your SIM card. Now it's way beyond me how it's happened but out of the 3 iPhones I have I only have the original box for one of them and the pin is missing.
So how can I open up the SIM card slot of an iPhone without the pin. I tried a toothpick but it's too fat to fit into the hole.
I have whittled a wooden pin from a piece of wood once - it was strong enough to push out the SIM holder, but I wouldn't want to use that repeatedly, as I was worried it would break inside the ejection slot.
As said a paperclip or a safety pin is your best bet. I used them occasinally. Even if you have colorful paper clips (a bit thicker than normal) you can strip the plastic with scissors.
When I had an iPhone, I used to use my glasses since they were thin enough.
I always use the back of earrings to open SIM card slots as well as press the small reset holes in some technical devices. They mostly have the right size to fit into the hole and the probability that I have one with me all the time is high. You have to be carefull not to bend them though.
I have actually was able to open the sim card slot using a toothpick however any object that is small enough to fit in the tiny hole will do just be careful with the amount of pressure you apply as much is not needed to spring the tray.