In order to use your new smartphone or iPhone, you will need a SIM card of the correct size.
There are currently 3 SIM formats in used:
The Mini SIM
The most common SIM card format is 25 mm x 15 mm in size. The SIM card consists of a chip and a plastic frame. By cutting the plastic frame of the Mini-SIM you can transform it into a Micro-SIM.
The micro-SIM is a smaller version of the Mini-SIM. The only difference lies in the size. The micro-SIM was seen for the first time on the iPhone/iPad, since then several manufacturers have followed the trend.
The nano-SIM is the smallest variant of the SIM card. It has the following dimensions 12.3 x 8.8 x 0.67 mm and is thinner than any of their predecessors. The nano-SIM was first used in the iPhone 5.