Although not widely used, the advantage of an eSIM is that it allows you to change phones without transferring SIM cards the mobile operator transfers the account information remotely. eSIM: An embedded SIM, or eSIM, is a new, emerging format in which the SIM is embedded directly into the device and is therefore not removable.It has a smaller contact surface, making it physically incompatible with older phones that expect a micro-SIM. Nano-SIM: This is the smallest SIM format in use today.Micro-SIM: A micro-SIM has the exact same contact surface but is smaller (15x12mm) because the plastic is trimmed away, leaving a card almost entirely of just the contact surface.It measures 25x15mm and the contact surface is surrounded by a large segment of plastic. Mini-SIM: Because the full-size SIM is no longer used, these days this is often thought of as the full or standard SIM.Despite the large size, virtually all of it was a plastic card - the actual contact surface was the same as later cards. Full SIM: No longer in use, the original SIM card was developed in the 1990s and measured 86x54mm. A SIM card is a card with a chip, which is used in mobile radio technology to identify a mobile device and its unique mobile phone number within its network.Today there are several kinds of SIM cards: SIM cards need to fit in mobile phones, so as time has progressed, there has been a need for smaller cards as phones have become increasingly thin and filled with larger batteries and more sophisticated electronics. If you change phones, as long as you keep the SIM card, these contacts and text messages will come with you to the new phone. SIM cards can carry a great deal of data, like your contact list and text messages. These let the network know what your phone number is, and what phone carrier you use (T-Mobile, Verizon, etc.).
Most SIM cards are provided by phone companies, and contain some basic identifying information like serial numbers and identifying codes.
A SIM card identifies you on the wireless network.