VoLTE SIM cards, PSTN replacement, 2G and 3G sunset guidance, HD voice technical reference, and VoNR. Everything engineers and specifiers need in one place.
VoLTE (Voice over LTE) is the 3GPP-standardised method for carrying voice calls over a 4G LTE network using the IP Multimedia Subsystem (IMS). Defined in GSMA IR.92, it delivers HD audio via the AMR-WB codec and eliminates the need to fall back to 2G or 3G for voice calls.
VoLTE stands for Voice over LTE. It is the 3GPP-standardised way to carry voice calls entirely over a 4G LTE network using the IP Multimedia Subsystem (IMS). Before VoLTE, a 4G phone making a voice call would drop back to 2G or 3G – a process called Circuit Switch Fallback (CSFB). VoLTE eliminates that fallback entirely.
The practical results are faster call setup (under 2 seconds vs 6-8 for CSFB), HD voice quality via the AMR-WB codec, and the ability to use data at full 4G speed during a call.
With all UK 3G networks now closed, VoLTE is not optional – it is the only way to make voice calls on a 4G-only device or SIM.
Technical reference for engineers, installers, and specifiers who need to understand VoLTE.
Not all SIMs support VoLTE. A SIM must carry ISIM credentials and be provisioned for IMS services by the operator. Standard IoT data SIMs do not qualify.
The UK PSTN closes in January 2027. Lifts, alarms, fire panels, and telecare devices that rely on analogue lines need a replacement path – often VoLTE via a cellular gateway.
All four UK operators completed their 3G switch-offs in 2024. Devices that relied on 3G voice must migrate to VoLTE. There is no circuit-switched voice on 4G.
Every modern UK smartphone supports VoLTE, but activation depends on carrier provisioning, handset approval lists, and correct SIM configuration.
Industrial routers and IoT devices need specific LTE modules with an IMS stack to support VoLTE. Most Cat-M1 and NB-IoT modules do not qualify.
VoNR (Voice over New Radio) is VoLTE’s successor on 5G Standalone networks. It uses the same IMS core but delivers voice over the 5G NR air interface with the EVS codec.