Glossary · VoLTE
What is VoLTE (Voice over LTE)?
VoLTE (Voice over LTE) is a packet-switched voice service that carries calls as IP data over a 4G LTE network using the IP Multimedia Subsystem (IMS) for call control, rather than the older circuit-switched 2G/3G channels. It delivers HD voice, faster call setup, and simultaneous voice-and-data over a single LTE connection — the mobile-network counterpart to the VoIP that powers cloud business phone systems.
How VoLTE works
A VoLTE call is signalled with SIP and IMS, the same session-control layer used in enterprise VoIP. When you dial, the handset sends a SIP INVITE carrying a Session Description Protocol (SDP) offer that lists the preferred voice codec — typically AMR-WB for HD voice — plus IP addresses and ports.
The voice itself rides a dedicated LTE bearer. Conversational voice media is carried on a guaranteed-bit-rate bearer marked QCI 1, while IMS signalling uses a separate QCI 5 bearer, so voice packets get low-latency priority over best-effort data on the same connection.
VoLTE key facts
VoLTE is defined by GSMA and 3GPP standards rather than a single proprietary spec:
| Attribute | Detail |
|---|---|
| Network | 4G LTE access, packet-switched |
| Control layer | IMS with SIP / SDP signalling |
| Primary profile | GSMA IR.92 (Voice over IMS over LTE) |
| 3GPP origin | Release 8, emergency voice in Release 9 |
| HD voice codec | AMR-WB (16 kHz wideband); AMR-NB fallback |
| Voice bearer | QCI 1 (guaranteed bit rate) |
| Signalling bearer | QCI 5 (non-GBR) |
AMR-WB samples at 16 kHz, the same wideband range that makes desk-phone codecs like G.722 sound clearer than narrowband telephony — which is why both are marketed as “HD Voice.”
VoLTE vs. VoIP
VoLTE and VoIP both send voice as IP packets and both use SIP/IMS for signalling, so the distinction is about the network underneath:
| Dimension | VoLTE | VoIP |
|---|---|---|
| Network | Carrier 4G LTE | Any IP / internet link |
| Devices | Built into mobile handsets | Softphones, desk phones, apps, browsers |
| QoS | Prioritised carrier bearer (QCI 1) | Best-effort, depends on the connection |
| Business integration | Carrier-level, limited | Deep CRM, API, and app integration |
VoIP is the foundation of cloud business phone systems because it runs on any IP connection and integrates with software workflows. VoLTE is essential on mobile because carriers are retiring 2G and 3G, leaving LTE and 5G — where VoLTE carries voice — as the only path for calls.
Where VoLTE fits for business phone
For a VoIP business phone system, VoLTE matters at the mobile edge. When a team member uses a carrier mobile number or a dual-SIM work phone, that leg of the call is carried by VoLTE on the mobile network. A softphone app on the same device instead uses the data connection (over LTE, 5G, or Wi-Fi) to reach the cloud VoIP platform via SIP — independent of whether the carrier voice service is VoLTE.
The practical takeaway: VoLTE governs the carrier’s native dialer call quality, while your business phone app rides the data path. Both can deliver HD voice when wideband codecs negotiate end to end, and both fall back to narrowband at any legacy hop.
VoLTE (Voice over LTE) frequently asked questions
What is VoLTE in simple terms?
VoLTE (Voice over LTE) is a way of making phone calls as IP data over a 4G LTE network instead of the older 2G/3G voice channels. It uses the IMS call-control layer with SIP signalling and an HD voice codec, so calls sound clearer, connect faster, and let you use voice and data at the same time on one LTE connection.
What is the difference between VoLTE and VoIP?
Both send voice as IP packets and both use SIP/IMS for signalling. The difference is the network underneath. VoLTE runs over a carrier’s 4G LTE network with a prioritised bearer for voice.
VoIP runs over any internet connection and powers cloud business phone systems with deep software, CRM, and API integration. VoLTE is built into mobile handsets; VoIP runs on softphones, desk phones, and browsers.
Does VoLTE provide HD voice?
Yes. VoLTE typically negotiates the AMR-WB (Adaptive Multi-Rate Wideband) codec, which samples voice at 16 kHz for wideband HD audio, with the narrowband AMR-NB codec as a fallback. Both endpoints must support the wideband codec for the call to ride HD voice end to end.
What standards define VoLTE?
VoLTE is based on the GSMA IR.92 profile for Voice over IMS over LTE, which builds on 3GPP specifications. Most VoLTE interface requirements came from 3GPP Release 8, with features like emergency voice calls over LTE added in Release 9. It uses IMS for call control and dedicated LTE bearers (QCI 1 for voice, QCI 5 for signalling) for quality of service.
Does a VoIP business phone system need VoLTE?
Not directly. A cloud VoIP business phone app reaches the platform over the device’s data connection (LTE, 5G, or Wi-Fi) using SIP, independent of the carrier’s VoLTE voice service. VoLTE governs the quality of the carrier’s native dialer calls, while the business phone app rides the data path for its own routing, recording, and CRM features.
See how DialPhone fits
DialPhone’s business phone is a cloud VoIP platform: calls ride SIP over whatever IP path the device has — LTE, 5G, or Wi-Fi — and negotiate wideband HD voice when both endpoints support it. VoLTE handles the carrier’s native mobile calls; DialPhone handles your business numbers, call routing, and CRM logging on top of the same modern IP networks.