VoLTE SIM Cards

Key point

A SIM is not automatically VoLTE-capable. It must carry an ISIM application on the UICC and be provisioned by the operator with IMS Private Identity (IMPI) and IMS Public Identity (IMPU). Standard IoT data SIMs, M2M SIMs, and many older SIMs do not meet these requirements.

What the SIM must contain

A VoLTE-capable SIM is a UICC (Universal Integrated Circuit Card) that contains both a USIM application (for LTE authentication) and an ISIM application (for IMS authentication). The ISIM stores:

IMPI (IMS Private Identity) – a permanent identifier used internally within the IMS for authentication, formatted as an NAI (Network Access Identifier)
IMPU (IMS Public Identity) – the addressable identifier used to route calls to the subscriber, formatted as a SIP URI (sip:+447700900123@operator.com) or tel URI
P-CSCF address or the mechanism to discover it (via PCO – Protocol Configuration Options)
IMS service profile entitlements – the flags that grant access to voice, video, and messaging services via the IMS

UICC Application Structure – VoLTE SIM vs Standard IoT SIM

Standard IoT SIM (UICC) USIM IMSI, Ki, LTE authentication No ISIM No IMS credentials Data-only profile No voice entitlement Does NOT support VoLTE

UK operator VoLTE SIM support

Operator	VoLTE launched	Consumer SIMs	IoT/M2M SIMs	MVNO coverage
EE	2015	All SIMs issued since 2016	Available on request	MVNOs vary by agreement
Vodafone	2016	All current SIMs	Available on request	MVNOs vary by agreement
O2	2016	All current SIMs	Available on request	MVNOs vary by agreement
Three	2016	All current SIMs	Limited availability	MVNOs vary by agreement

IoT SIMs and VoLTE

IoT and M2M SIMs are typically provisioned for data only. They carry a USIM but not an ISIM. Even if the LTE module in a device technically supports VoLTE, the call will fail if the SIM does not have IMS credentials provisioned.

This is the most common cause of VoLTE failure in industrial installations. The engineer confirms the device supports VoLTE, the network has VoLTE active, but the SIM is a standard data SIM without ISIM. No call.

Common mistake
Using a standard IoT data SIM in a PSTN replacement unit, lift phone, or alarm dialler and expecting VoLTE to work. It will not. The SIM must be explicitly provisioned for IMS voice services. Ask your SIM supplier specifically for a VoLTE-capable SIM.

What to ask for when sourcing a VoLTE SIM

Confirm the UICC carries an ISIM application
Confirm IMS Private Identity (IMPI) and Public Identity (IMPU) have been provisioned in the HSS
Confirm the service profile includes voice bearer entitlement (not data-only)
Confirm VoLTE is active in the coverage area of the installation
For roaming deployments: confirm VoLTE roaming is supported between home and visited network
Test an actual VoLTE call on the target device and SIM combination before site deployment

What the SIM must contain

UK operator VoLTE SIM support

IoT SIMs and VoLTE

What to ask for when sourcing a VoLTE SIM

Need a VoLTE SIM for your project?