A SIM card stores your subscriber identity data, which is needed to connect to a carrier's network. But do you still need one in 2025?

Have you ever wondered exactly how a SIM card works? We'll help you understand why your phone needs one and what they do to keep you connected.

In this Ask Maggie, CNET's Marguerite Reardon advises a reader looking to use a SIM card from a tablet to get data-only wireless service on his smartphone.

Insurance tracking devices can be mysterious, so we look at what an insurance tracker is, what data it gathers, and how it's used to set your car insurance rates.

SIM cards link accounts to handsets. They keep communications private. They store messages. Although small and simple, they are a big part of modern mobile phone systems.