Apple's iPhone 4 and iPhone 4S use a micro SIM, which measures just 15x122mm, rather than a traditional sized SIM that measures 25x15mm. It is also located in a different place than previous models of the iPhone. We show you how to insert the SIM into your iPhone 4.
Contained within the manual for your iPhone is a small pin designed for use in removing the micro-sim. However, if you're not in possession of this, a bent paper clip will do the same job. Insert this into the tiny whole located on about half-way up on the right-side of the handset to remove the Micro-SIM tray.
Insert the SIM, contact side down into the tray and then push it back into the smartphone. It will click when it has been fully inserted. Now switch the phone on and wait for it to boot-up.