A RUIM card (also R-UIM) or Re-Usable Identification Module, is a removable ID chip for cellular phones made for the Code Division Multiple Access (CDMA) network. The RUIM card holds a user's personal information such as name and account number, cell phone number, phone book, text messages and other settings.

The RUIM card provides flexibility to switch phones by simply removing the RUIM card and slipping it into another card-enabled phone. The new phone would then be able to make and receive calls on the user's account without having to go through the carrier for activation. A user could, for example, have several phones and switch between them, borrow a friend's phone to make a call with his RUIM card, or even switch to another carrier and keep his or her old phone. The new carrier would simply issue the customer a new RUIM card to use in his or her existing phone. The only requirements are that the phone is unlocked and compatible with the frequency band of the new carrier.

Although the idea of a RUIM card might be new to people who have had cellular service with a CDMA carrier, the concept is old hat to those using Global System for Mobile Communication (GSM) networks. GSM is a competing network technology, popular in Europe and most countries outside of North America with a much larger overall share of the world market. GSM phones use a Subscriber Identify Module or SIM card. SIM cards and RUIM cards will be interchangeable in phones, allowing the consumer maximum flexibility. They will also be required to meet the same standards, facilitating uniform manufacturing standards.

Savvy CDMA users in the United States have been anxiously awaiting the arrival of RUIM cards, particularly since GSM has become more competitive in the American market. The SIM card used with GSM phones offers many distinct advantages to the consumer over the traditional proprietary handsets required by CDMA technology. A RUIM card would make CDMA more attractive to consumers and would also open the door to better roaming contracts between CDMA and GSM networks, allowing the best possible global coverage for all cellular customers.

The RUIM card was developed by the CDMA Development Group and 3rd Generation Partnership Project (3GPP). It was approved by the Telecommunications Industry Association (TIA) and has been used in China since 2002.