---
title: How GSM SIM cards work
description: A SIM card is a small, flat, plastic card that transmits signals and information from telecom carriers (phone companies, like FreedomPop to communication devices (phones, tablets, and mobile hotspots)
---

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# How GSM SIM cards work

**What’s a SIM card?**

A SIM card is a small, flat, plastic card that transmits signals and information from telecom carriers (phone companies, like FreedomPop to communication devices (phones, tablets, and mobile hotspots).

SIM stands for Subscriber Identity Module and SIM cards typically, but not exclusively, contains the following information:

- A phone number
- Contact lists
- Network authorization data
- Calling history
- Text messages

When you buy a SIM card from FreedomPop, and insert that SIM card into a compatible phone, FreedomPop can supply your phone with an internet connection and cellular (calling and texting) services. SIM cards can only transmit signals to phones that are open to read and receive those signals.

Locked phones (phones that are set to work only with certain carriers, like T-Mobile or Verizon) cannot read the information on our SIM cards. So it's important the phone you're using is **unlocked**. 

 

**Compatible phones**

Our talk, text, and data SIM cards work with GSM unlocked, Android, and iOS smartphone devices. 

Want to know more about compatible phones? [Read this](https://help.freedompop.com/phones-that-are-compatible-with-our-lte-sims?hsLang=en). 

 

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