VoLTEAlso known as Voice over LTE, 4G calling, HD Voice

How VoLTE works

A VoLTE phone registers with the operator’s IMS core using SIP, much like a VoIP phone registers with a PBX. When a call starts, the network creates a dedicated LTE bearer with QoS class identifier (QCI) 1 for the voice RTP stream and QCI 5 for signalling, so voice keeps priority over data. The service profile is defined by the GSMA in IR.92.

• HD voice: AMR-WB (wideband) is standard; EVS extends to super-wideband.
• Faster call set-up than circuit-switched fallback (CSFB) to 3G.
• Simultaneous voice and 4G data.

On 5G standalone networks, the equivalent is VoNR (Voice over New Radio), which uses the same IMS core.

Why VoLTE matters after 2G/3G shutdowns

As operators retire 2G and 3G, any phone or gateway without VoLTE loses the ability to make ordinary calls. Classic GSM gateway modules that only support circuit-switched voice stop working on those networks. VoLTE must also be supported by both the device and the operator for that specific model, and is often a prerequisite for VoWiFi on the same phone.

VoLTE and phone-based gateways

Because GSMCalls uses ordinary modern phones as gateways, calls go out over whatever the phone and operator support, including VoLTE and Wi-Fi Calling, rather than depending on 2G/3G modules. Check tested models on the compatibility page and read VoLTE and Wi-Fi Calling for GSM gateways.