TRC Facilitates VoLTE and IMS Interoperability Between Operators

In 2026 the Cambodian authorities addressed the interoperability of voice over LTE (VoLTE) services and of the underlying IP multimedia subsystem (IMS) architectures used by mobile operators. The measures respond to the transition away from legacy circuit-switched voice networks, to the growing importance of high-quality voice as a differentiated service and to the need for reliable voice interconnection between operators as the sector completes its migration.

The measures are relevant to mobile network operators, to interconnection providers, to enterprise customers with voice-intensive requirements and to equipment vendors supporting the transition.

VoLTE delivers voice as an IP service over LTE networks, using the IMS architecture. Compared with circuit-switched voice, it offers improvements in voice quality, faster call setup, integration with other IMS services and more efficient use of network resources. Operators have progressively deployed VoLTE, and the transition is being accelerated by the withdrawal of legacy 2G and 3G services in some markets.

Interoperability between operators is essential to preserve the ability of subscribers to make and receive voice calls across networks. Historically this has been achieved through circuit-switched interconnection, but with the transition to VoLTE, IP-based interconnection between IMS networks is becoming the norm.

The measures pursue several objectives, including the maintenance of high-quality voice services across the sector, the continuity of voice interconnection between operators, the preservation of features such as emergency calling and lawful cooperation, and the smooth transition away from legacy networks. They aim to align operators on a common set of expectations without imposing detailed technical prescriptions that could constrain innovation.

The measures also address customer-facing considerations, including the availability of information to subscribers about VoLTE, the handling of devices that are not VoLTE-capable and the impact of the transition on legacy services such as voice roaming.

Interoperability between IMS networks relies on adherence to internationally recognised standards for signalling, media codecs, security and interconnection interfaces. The measures reinforce these standards as the basis for Cambodian arrangements, encouraging operators to align their deployments with recognised profiles and to cooperate on any adaptations required to reflect specific national considerations.

Coordination between operators on the details of interconnection, including the specific codecs supported, the handling of specific call scenarios and the treatment of supplementary services, supports smooth end-to-end operation.

Interconnection between IMS networks requires commercial arrangements that reflect the technical characteristics of IP-based interconnection. Reference offers, service level commitments, arrangements for capacity provisioning and mechanisms for dispute resolution should be adapted to the IMS context. Existing frameworks for circuit-switched interconnection can inform these arrangements but should not be applied mechanically.

Operators are expected to negotiate in good faith, to publish appropriate reference terms and to cooperate with the regulator in the event of disputes. The regulator may intervene where necessary to preserve effective interconnection.

Emergency calling remains a central obligation. Operators are expected to ensure that VoLTE emergency calls are routed correctly, that appropriate location information is provided where technically feasible and that arrangements exist for handling emergency calls from devices that are not VoLTE-capable. Coordination with emergency services and with other operators is important.

Other specialised services, including lawful cooperation, accessibility features and services for enterprise customers, should also be supported over VoLTE in a manner consistent with the corresponding obligations that applied to circuit-switched services.

Consumers should be informed about the transition to VoLTE, about the benefits it offers and about any implications for their existing devices. Devices that do not support VoLTE may lose access to voice services on networks that have decommissioned legacy voice. Operators are expected to provide reasonable notice and, where appropriate, support to affected subscribers.

Retail sales of new devices should reflect the transition, so that customers acquire devices that will remain functional over the medium term. Coordination with device manufacturers and with the type approval framework supports the availability of appropriate devices.

Enterprise customers with voice-intensive requirements, including contact centres, financial institutions and public sector organisations, may need to adapt their internal systems to work effectively with VoLTE-based mobile voice. Coordination between mobile operators and enterprise IT teams, together with attention to interoperability with enterprise PBX systems and unified communications platforms, supports smooth operation.

For enterprises that rely on legacy device fleets, transition planning is important to avoid disruption when legacy voice is decommissioned. Timely renewal of devices and testing of interoperability with enterprise applications reduce operational risk.

For operators, the measures call for a coherent programme covering technical deployment, interconnection arrangements, commercial contracts, consumer communication and enterprise engagement. Governance arrangements should ensure that the different aspects are coordinated and that risks associated with the transition are identified and managed.

For enterprise customers, the measures reinforce the value of active engagement with operators, of internal testing and of transition planning that reflects the timelines communicated by operators.

Lex Civora advises mobile operators, interconnection providers and enterprise customers on the interpretation and application of the VoLTE and IMS interoperability measures, on the negotiation of interconnection arrangements and on the management of the transition away from legacy voice networks in Cambodia.

The transition to VoLTE has implications for the way in which numbers, identities and services are managed in IMS-based networks. Subscriber profiles, presence information and identity data are handled differently from legacy circuit-switched arrangements, and operators should review their systems to ensure that numbering, presentation of calling line identity and interaction with number portability continue to operate correctly across all call scenarios.

Coordination between operators on identity-related aspects of interconnection, including trust arrangements for calling line identity across networks, supports customer confidence and helps reduce the risk of fraud that exploits weaknesses in identity presentation.