For those of you that are often switching devices like us and want to use that same SIM card on another phone, you’d need one of those adaptors you see on the left. It also shows just how much smaller the new nano SIMs are than existing micro SIM cards and the standard SIM card.
To get an even better idea about the size of these new cards, below there is a micro and nano SIM cards compared to the size of coins.
Carriers should be already stacked with the new nano SIM cards, but we’d definitely get one of those adaptors as well just in case while shopping for that new iPhone 5.
source: Engadget, Vodafone