CdmaOne in the context of "2G"

3G refers to the third generation of cellular network technology. These networks were rolled out beginning in the early 2000s and represented a significant advancement over the second generation (2G), particularly in terms of data transfer speeds and mobile internet capabilities. The major 3G standards are UMTS (developed by 3GPP, succeeding GSM) and CDMA2000 (developed by Qualcomm, succeeding cdmaOne); both of these are based on the IMT-2000 specifications established by the International Telecommunication Union (ITU).

While 2G networks such as GPRS and EDGE supported limited data services, 3G introduced significantly higher-speed mobile internet and enhanced multimedia capabilities, in addition to improved voice quality. It provided moderate internet speeds suitable for general web browsing and multimedia content including video calling and mobile TV, supporting services that provide an information transfer rate of at least 144 kbit/s.

The international mobile subscriber identity (IMSI; /ˈɪmziː/ IM-zee) is a number that uniquely identifies every user of a cellular network. It is stored as a 64-bit field and is sent by the mobile device to the network. It is also used for acquiring other details of the mobile device in the home location register (HLR) or as locally copied in the visitor location register. To prevent eavesdroppers from identifying and tracking the subscriber on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated TMSI is sent instead. Mobile phone identities and data are sometimes scooped up by equipment called an IMSI-catcher or Stingray phone tracker that mimics cellular networks, creating serious privacy and other human rights concerns.

The IMSI is used in any mobile network that interconnects with other networks. For GSM, UMTS and LTE networks, this number was provisioned in the SIM card and for cdmaOne and CDMA2000 networks, in the phone directly or in the R-UIM card (the CDMA equivalent of the SIM card). Both cards have been superseded by the UICC.

CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible successor to second-generation cdmaOne (IS-95) set of standards and used especially in North America and South Korea.

CDMA2000 compares to UMTS, a competing set of 3G standards, which is developed by 3GPP and used in Europe, Japan, China, and Singapore.