The physical compatibility of Subscriber Identity Modules (SIMs) between Android and iOS devices is generally standardized. Most modern smartphones, regardless of the operating system, utilize a Nano-SIM card. Therefore, a SIM card physically extracted from an Android phone can usually be inserted into an iPhone, and vice versa, provided both devices are unlocked and support the same cellular network frequencies.
The significance of this compatibility lies in user convenience during device transitions. Historically, switching between operating systems could involve obtaining a new SIM card, potentially requiring a new service agreement and phone number. The current standardization simplifies this process, enabling users to retain their existing phone number and cellular service when migrating from an Android device to an iPhone, or the reverse.