The VAS Experts solution implements various integration scenarios, including for MVNOs and small operators.
Enabling the IMS context on the network and allowing Voice-over-PS (VoLTE and VoWiFi) is required. For MVNOs, this requires interaction with the host operator and debugging the interaction. This can take 1-3 months.
If VoLTE is already launched by the operator, implementing VoWiFi is much easier.
WiFi Calling may require changes to the SIM configuration. Generally, this can be done via OTA.
VAS Experts will provide SIM configuration rules.
This is the longest part of the process; we recommend starting it immediately after deciding to implement ePDG.
Support for your operator with enabled VoLTE and VoWiFi options should appear in the phone and modem configuration (CarrierConfig). This can only be done by phone manufacturers (Samsung, Honor, Lenovo, and many others). Without support for your operator (by PLMN code on the SIM), the phone ignores these options.
VAS Experts will help optimize the interaction process with vendors.
It is important that WiFi Calling only works on relatively new phone models, not the most budget models, with an operator's SIM that supports LTE. An approximate list of phones can be found on marketplaces with the WiFi Calling filter, for example, here.