The evolution of the SIM card has been rather brisk in the last few years. The full-sized SIM is 85.60 mm by 53.98 mm by 0.76. The Micro-SIM, as used in the iPhone 4 and 4S, is 15.00 mm by 12.00 mm by 0.76 mm. The Nano-SIM, as used by the iPhone 5, is a tiny 12.30 mm by 8.80 mm by 0.67 mm. So when it was announced by Apple that they would be moving to the Nano-SIM, many wondered if they could convert their Mirco-SIM to fit in the iPhone 5. Turns out, it may just work.
John Chan over at CNET Asia has taken it upon himself to not only trim down a current Micro-SIM, but he also did the needed sanding to get the depth of the tiny card within spec. With his testing, it seems to work fine when he inserts it back into the original phone. That said, it isn’t a guarantee that it will work in the iPhone 5, so don’t get to snipping and sanding just quite yet. Before you do anything drastic, just wait until confirmation from actual iPhone 5 users that trimmed Micro-SIMs do work.
Even better, contact your carrier of choice, and ask if they will provide you with a Micro-SIM. Your mileage may vary depending on carrier and country of choice, but it is worth it to get the due diligence out of the way before you break out the power tools.