SIM cards are small, removable smart cards used in mobile phones and smartphones to store data such as your mobile phone number, your telephone company, your billing information and in some cases your address book.
eSIM and iSIM explained
SIM cards (short for Subscriber Identity Module) can be removed from one phone and inserted into another. This makes it easy to transfer phone service and address book information to new phones. All you have to do is swap the card into a new phone.
Because SIM cards are interchangeable, they are also useful for international travel. If your phone is compatible with the mobile networks in the country you are visiting, you can buy a new SIM card in another country, put it in your phone and make calls and use data like a local. This is cheaper than using an international data plan.
Not all phones have SIM cards. Other phones do, but you can't remove them.
