microSIMs

Micro-SIM is a removable smart card used in mobile devices to identify a subscriber on a cellular network. It stores the credentials used to authenticate with a mobile operator and can be swapped between devices. The micro-SIM measures 15 by 12 millimeters and is part of the 3FF family of SIM card sizes. It was designed as a mid-size option between the earlier mini-SIM (2FF) and the later nano-SIM (4FF).

Introduced in the mid-2000s by the European Telecommunications Standards Institute, the micro-SIM gained widespread use in smartphones in the 2010s, with the iPhone 4 notable for adopting the format. In the following years, many manufacturers shifted toward even smaller nano-SIMs, and some devices continued to ship with micro-SIM trays for longer. As of the mid-2010s, both micro-SIM and nano-SIM were in use, depending on the model and carrier.

In modern devices, the trend toward eSIM technology reduces or eliminates the need for a physical SIM in some markets, though micro-SIMs remain common in devices that still rely on removable SIM cards. A micro-SIM can store essential data such as the IMSI, authentication keys (Ki), and related network information, along with optional contacts or carrier data. Handling and adapters exist to use micro-SIMs in devices designed for other SIM sizes, but care must be taken to avoid damage or data loss.