For my trip to Rome, I called up my wireless provider and had my plan changed to an international calling plan so my grandma and I could call home. However, when I arrived I was sorely without service. After much frustration and calls to my provider (using Skype! <– very important to have while traveling), they deduced that my issue was because they had the wrong SIM number for my account.
Fixing this required that I be able to give them my actual SIM number, and on my iPhone 4S you have to do this by popping out the SIM tray. When you received your phone you were given a little key that looks like an oval with a little stick, and I, like most people, do not carry this around with me. I tried a pen and it was too big, I tried a needle and it was too thin, and then my sister told me to use my earring! It worked and felt like a spy pulling out a high-tech gadget disguised as a normal object.
I made a little tutorial video to show you how simple it is! Just one extra tip: Always have your iPhone or iPad switched off while removing and inserting the SIM card!