Are you in the market for an unlocked iPhone 5 and need to fit your existing SIM card in it? You can actually cut your current SIM card down to nano size at home.
Most people won't need to do this, but if you've bought an unlocked iPhone 5, you can convert your current micro-SIM card into a nano-SIM with nothing but a pair of scissors. There are plenty of guides for this, but we really like this one from TechnoBuffalo, which provides a template that you can print out and size up exactly.
Note that some guides say you need to sand the cards thickness down too, but this isn't really necessary. Check out the video above from iPhoneZen to see what the process entails, and hit the link below to read more.
Printable Guide for Cutting MicroSIM to Nano-SIM for iPhone 5 [TechnoBuffalo]