VoLTE in Routers and IoT Devices
Most LTE modules used in industrial routers and IoT devices – particularly Cat-M1, NB-IoT, and low-cost Cat 1 modules – do not include the IMS firmware stack required for VoLTE. VoLTE in an industrial device requires a module that explicitly lists IMS/VoLTE support, plus a SIM provisioned with ISIM credentials.
Module compatibility
VoLTE in an IoT or router application requires a cellular module with:
- IMS stack in firmware (handles SIP REGISTER and INVITE)
- SIP client capability
- Dedicated QCI 1 GBR bearer support
- AMR-WB codec support in the audio path
- Audio interface (PCM, I2S, or USB audio) to connect a voice endpoint
| Module category | Typical examples | VoLTE support | Notes |
|---|---|---|---|
| Cat 1 bis (voice-capable) | Quectel EC21, EC25, EG25 | Yes – with IMS firmware | Must confirm IMS option in firmware |
| Cat 4 / Cat 6 (voice-capable) | Quectel EC200A, SIMCom SIM7600 | Yes – with IMS firmware | Commonly used in PSTN replacement gateways |
| Cat-M1 (LTE-M) | Quectel BG95, BG77, u-blox SARA-R4 | No – data only | No IMS stack; designed for IoT data |
| NB-IoT | Quectel BC66, BC660K | No | Data only; no voice bearer |
| 5G SA modules | Quectel RM520N, Fibocom FM350 | VoNR capable (when network available) | Requires 5G SA network |
PSTN replacement gateways
A class of device specifically designed for PSTN replacement uses a cellular module with VoLTE capability and presents an analogue RJ11 interface to existing telephony equipment. These cellular ATA (Analogue Telephone Adapter) style devices are the primary use case for VoLTE SIMs in the B2B market.
Common applications using cellular PSTN replacement gateways with VoLTE:
- Lift emergency phones – BS EN 81-28 requires two-way communication; VoLTE via cellular is the standard replacement for PSTN connections
- Intruder alarm diallers – registered alarm systems require an ARC-connected communicator; voice-path diallers need VoLTE
- Fire panel voice communicators – some Grade D systems use voice reporting; cellular VoLTE replaces the PSTN link
- Lone worker devices – personal emergency devices use voice calls to response centres
- Telecare and PERS units – vulnerable person alarm systems that trigger voice calls to care lines
Teltonika and VoLTE
Teltonika Networks produce industrial cellular routers, some of which include voice capability via compatible LTE modules. The TRB245 and TRB500 devices, for example, include audio interfaces and can support VoLTE where the module firmware includes the IMS stack and the SIM is appropriately provisioned.
For any Teltonika device being used for voice: confirm the specific module variant supports VoLTE (not all module configurations do), confirm the firmware has IMS enabled, and test with a VoLTE-provisioned SIM before deployment. A standard IoT data SIM will not work.