UICC: the chip we call a SIM card
UICC (Universal Integrated Circuit Card) is the technical name for the smart card we call a SIM card. It runs the SIM application (for GSM) and USIM (for 3G, 4G and 5G), which identify the subscriber. The embedded version, eUICC, is the basis of eSIM.
In plain words
A UICC is like a blank school planner, and SIM and USIM are like entries in it from different teachers (2G and 3G-5G networks). The planner itself is the "physical" card, and the entries are programs that let the network recognise you. An eUICC is a planner sewn right into the phone, where entries can be downloaded.
How it works
- A UICC is a microprocessor smart card with memory.
- It runs the SIM, USIM and ISIM applications.
- The USIM application stores the IMSI and keys for 3G/4G/5G.
- The card performs cryptographic checks when connecting to the network.
- An eUICC can download several operator profiles remotely.
Where you'll see it
In every modern SIM card and in the eSIM chips of phones, watches, tablets, cars and IoT devices. The term is mostly used in technical documentation.
Does it matter when buying
You do not need to know it. But it explains why an old SIM sometimes will not work on 4G: it may lack the USIM application - in that case get it replaced free by your operator.
Myths
- Myth: SIM and UICC are different cards. Reality: UICC is the physical card; SIM is one of the applications on it.
- Myth: eSIM is a completely different technology. Reality: An eSIM is an embedded eUICC.
FAQ
Why won't my old SIM work on 4G?
It may not have USIM - get your SIM replaced by your operator.
What is an eUICC?
An embedded UICC that can download profiles - the basis of eSIM.
What is ISIM?
An application for services like VoLTE on some networks.