Long-Term Evolution (LTE) is the 4G evolution of the 3G + Universal Mobile Telecommunications System (UMTS). Notably, it replaced both UMTS, + which descended from the 2G Global System for Mobile Communications (GSM), as well as the 3G + Code-Division Multiple Access 2000 (CDMA2000), which was the main competitor to UMTS. + For the first time, this meant that cell phone networks worldwide coalesced around a single protocol, removing the need for world travelers to carry a phone with dual radios. + One reason LTE was able to achieve this was by supporting a mixed-mode network, where CDMA2000 (or UMTS) was used for voice calls and LTE for data communications. + This provided a seamless upgrade path for cell phone operators. Over time, most carriers eventually switched to Voice over LTE (VoLTE).
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