VoLTE is a feature allowing your device to stay connected via LTE (4G) while making voice calls.
This feature is only available on some handsets, and in some global regions. Enabling this setting allows VoLTE to be used by mobile network providers that support this feature. If your network does not support VoLTE, it won't be used and calls will continue to be made via 3G.
Traditionally, LTE is set up as a complement to a 3G network, so that phones can use LTE while using data, and drop back to a 3G connection when making a voice call. This was done for ease of implementation, but imposes some restrictions:
- You need to be within range of a 3G cell tower to use your phone, even if you can receive LTE.
- While a voice call is in progress, the phone cannot use LTE for data, dropping instead to a 3G technology for data (which may include HSPA+, HSDPA, etc), slowing down any ongoing data transfers.
- Making and answering a voice call is fairly slow and involves a noticeable delay, due not only to inefficiencies in 3G but to the switching between connections.
VoLTE relaxes these restrictions, allowing phones to connect only via LTE without requiring a 3G connection for basic phone use. The voice data is encapsulated inside a data stream sent over the LTE network. Most providers do not count this data towards quotas or usage.
While it is not a requirement of VoLTE, VoLTE is usually implemented alongside AMR-WB, also known as "HD Voice", providing better speech quality and a wider frequency response. The benefit of the improved speech quality can only be realized when communicating with another person whose device and connection also supports HD Voice.
HD Voice is not exclusive to VoLTE users, with some handsets and providers supporting it as an optional enhancement when using 3G.