How does a SIM card work? SIM card History and SIM card size :

SIM card size:

The Standard SIM card (15 x 25mm) is the oldest of them (introduce in 1996) and so while it was once used in many handsets, including big-name ones like the iPhone 3GS, it’s rarely used in phones now – some feature phones and very basic mobile phones still use these, as do some old handsets, but most smartphones made in the last five years won’t.

A Micro SIM card (12 x 15mm) is also an old SIM card. this card introduced in 2003 but manufacturers didn’t adopt it until 2010. It’s a little smaller than the Standard SIM card but the actual chip is the same size, so it’s just the bit around it that’s smaller.

Nano SIM card (8.8 x 12.3mm) is the smallest of the bunch, also the newest (introduce in 1996). This has almost no border around the chip so it’s hard to imagine SIM cards getting much smaller in future unless the chip itself is shrunk.