Can I use my iPhone 5 nano-SIM card in older iPhones?
In order to save space, the iPhone 5 uses a nano-SIM card, which is smaller than the micro-SIM cards found in older model iPhones. So what happens if you're interested in swapping out your iPhone 5 SIM card to use in an iPhone 4S, iPhone 4, iPhone 3GS, iPhone 3G or original iPhone 2G?
Luckily, third party manufacturers are bringing nano-SIM (4FF) card adapters to the market. These adapters increase the size of your nano-SIM card to micro-SIM (3FF), then you can slide them into the SIM card tray of your older iPhone. The nano-SIM measures just 12.3mm x 8.8mm x 0.67mm, however it's fully backward compatible with older SIM standards.
Adapter solutions even exist to use a nano-SIM card in a device that supports the older, larger mini-SIM (2FF) standard. If you're interested in swapping the iPhone 5 SIM card between devices, it's worth spending around 5 bucks on an adapter.