iPhone 5 uses a nano SIM, smaller than the micro-SIM of the iPhone 4 and 4S. Nano SIM Card is 40% smaller than the micro-SIM and measures 12.3mm wide, 8.8mm high, and 0.67mm thick.
The new Nano SIM is no way different, apart from the size, than the existing SIM cards and it offers the same functionality.
A Nano SIM card is required in order to use cellular services when connecting to GSM networks and CDMA networks. An iPhone that has been activated on a CDMA wireless network may also use a SIM card for connecting to a GSM network, primarily for international roaming.
You can follow the below given steps to insert nano SIM in your iPhone 3GS, iPhone 4, iPhone 4S, and iPhone 5.
How To Insert SIM Card In iPhone
1. Insert the end of a small paper clip or SIM eject tool into the hole on the SIM card tray.
2. Pull out the SIM card tray and place the SIM card in the tray as shown.
3. With the tray aligned and the SIM card on top, carefully replace the tray.
Indian telecom operators, Bharti Airtel, Vodafone India and MTNL Mumbai will be offering nano SIM cards to the customers in the Mumbai circle, ahead of iPhone 5 launch.