At first glance this seems to be just a design feature, but actually there is an important technical reason behind it which protects your phone from damage. The interesting thing is that there was a time when SIM cards were completely square, but later this cut corner became a global standard.
The story of SIM cards began in the early 1990s. Initially, SIM cards were as large as today's credit cards. As mobile phones became smaller, SIM cards also became smaller. First came the mini-SIM, then the micro-SIM, and finally the nano-SIM. Although the size changed, the cut corner of the SIM card remained the same. The European Telecommunications Standards Institute (ETSI) adopted it as a global standard so that SIM cards can be used in the same way around the world.
The biggest advantage of this cut corner is that it prevents users from inserting the SIM card incorrectly into the phone. The golden chip in the middle of the SIM card has to be inserted at the right place in the SIM slot of the phone. If the SIM is inserted in the wrong direction, not only the SIM card can be damaged, but the delicate SIM reader inside the phone can also be damaged. The cut corner acts as a guide, making it easier to insert the SIM correctly into the SIM tray.
This design is beneficial not only for the users but also for the mobile phone manufacturing companies. The phone's SIM tray and the slot inside are made according to this cut design. This almost eliminates the possibility of error during phone assembly. This is the reason why no person in any corner of the world can insert the SIM card wrongly in his phone.
Now, the trend of e-SIM in smartphones is gradually increasing. Some companies have already launched phones that do not have a slot for a physical SIM card. In these phones, the telecom operator activates a digital SIM. In the future, as e-SIM usage increases, traditional SIM cards may become a thing of the past.