Removable User Identity Module (R-UIM) is a card developed for CDMA handsets that extends the GSM SIM card to CDMA phones and networks. To work in CDMA networks, the R-UIM contains an early version of the CSIM application. The card also contains SIM (GSM) application, so it can work on both networks. It is physically compatible with GSM SIMs and can fit into existing GSM phones as it is an extension of the GSM 11.11 standard.
The card brings one of the main advantages of GSM to CDMA network phones. By having a removable identity card, CDMA users can change phones while keeping their phone numbers by simply swapping the cards. This simplifies many situations such as phone upgrades, phone replacements due to damage, or using the same phone on a different provider's CDMA network.
This form of card is widely used in China under the CDMA service of China Unicom(The CDMA service of China Unicom was acquired by China Telecom in 2008) . However, it is also used elsewhere such as India, Thailand, and Japan.