VoLTE stands for Voice over LTE, which is a high-speed wireless communication standard for voice calls using mobile phones and data terminals. It is a digital packet technology that uses 4G LTE networks to route voice traffic and transmit data. VoLTE has up to three times more voice and data capacity than older 3G UMTS and up to six times more than 2G GSM. It uses less bandwidth because VoLTEs packet headers are smaller than those of unoptimized VoIP/LTE. VoLTE calls are usually charged at the same rate as other calls.
VoLTE is based on the IP Multimedia Subsystem (IMS) architectural framework, with specific profiles for control and media planes of voice service. This facilitates VoLTE on the LTE network and enables the service to deliver multimedia as data flows using a common IP interface that can use but doesn't depend on a legacy circuit-switched voice network.
To use VoLTE, the device, its firmware, and the mobile telephone providers on each end, as well as the inter-carrier connectivity must all implement the service in the area, and be able to work together. VoLTE has been marketed as "HD Voice" by some carriers, but this is a broader concept. All major cellular carriers, including Verizon, are moving to VoLTE technology and will be retiring their own.
