As 2G and 3G networks are switched off, circuit-switched voice goes with them. On 4G and 5G, a voice call is a data session to an IMS. For an MVNO that means voice is no longer something the host network simply provides. Either the host operator gives you access to its IMS, or you run your own.
Running your own IMS is what gives an MVNO control over voice: your own numbering and routing, your own interconnect rates, your own supplementary services, and voice that keeps working when your subscribers roam.
IMS core. The call session control functions (P-CSCF, I-CSCF, S-CSCF) register handsets and route calls. This is the heart of VoLTE.
Subscriber data. The HSS holds IMS subscriptions and authentication data. It usually sits with the mobile core.
Telephony application server. Call forwarding, call barring, call waiting, caller ID presentation and the other supplementary services subscribers expect.
SMS over IMS. An IP Short Message Gateway delivers SMS over the same IMS registration, and interworks with legacy SMS where needed.
Emergency calling. Emergency calls must be recognised, prioritised and routed to the right answering point, including for subscribers without a valid registration.
Voice interconnect. SIP interconnect to carriers for calls to and from other networks, with routing and failover.
Charging. Online charging for prepaid, offline charging records for postpaid and wholesale settlement.
Lawful intercept and recording. A regulatory obligation in most markets, and one to plan for from day one.
VoWiFi. Calling over WiFi uses the same IMS, with an extra gateway in the packet core that terminates the secure tunnel from the handset.
Handset support is not automatic. Phones enable VoLTE per operator, based on a profile for your network code. Getting your profile into the major handset vendors takes time, so start early.
Roaming changes the picture. With home-routed VoLTE roaming, calls from roaming subscribers come back to your own IMS. That keeps the service consistent, but it means your IMS has to be reachable and sized for it.
Testing needs real devices. Simulators prove the signalling. Only real handsets on a real radio network prove that registration, calls and SMS work the way subscribers will use them.
A full MVNO typically owns the IMS, the application servers, messaging and charging, and takes the radio network from its host. Whether you also run your own mobile core depends on your agreement with the host operator.
We deliver the IMS, voice, messaging and charging as our own platform, and a 4G/5G mobile core through a specialist partner, as one integrated solution. You can take the whole stack, or only the voice and charging layer if you already have a core.
Carrier-grade telecom infrastructure built for performance. From mobile core networks to voice platforms — delivering your telecom service in real time.
