A SIM card or SIM (subscriber identity module) is a type of integrated circuit, often in the form of a smart card.

Jan 24, 2026 · What is a SIM card? SIM stands for “ Subscriber Identity Module,” and a SIM card is essentially the card that holds your carrier’s subscriber identity data.

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Learn how to buy one, install or replace it, and change or activate a SIM card/eSIM.

Apr 9, 2026 · Learn what a SIM card is, what it does, different SIM card sizes, and how they impact connectivity and performance.

What Is a SIM Card and How Does It Work? SIM cards house essential information for your mobile device to operate. Think of a SIM card as the heart of your mobile device: without it, you couldn't …

Choose a prepaid sim card for quick setup, or pick a mobile phone sim for a new line. You’ll find carrier-specific kits, clear plan details, and pickup or delivery options that fit your schedule.

Your phone's SIM card (or eSIM profile) is associated with a carrier, plan and billing account. To switch carriers, your device needs a new SIM (eSIM or physical card) to connect to a new network.

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How do I add a line to my AT&T Prepaid® account? How do I activate my prepaid phone? Can I switch to an AT&T Prepaid phone plan? Yes, you can switch your wireless phone to an AT&T Prepaid plan. …