In India, the TRAI (Telecom Regulatory Authority of India) recommended that providers will be allowed to offer app-based VoIP services through Wi-Fi.
Those calls will be considered the same way as classic calls. Thus the operators will have to have to follow the rules forme the TRAI.
The consequences are interesting for a country that can be subject to issues on phone connectivities to the network.
With this recommendation, you can now have the service from your regular provider with one phone number, and get the app of that same company, and use the same number for both. However, you can also download the app from another provider and get another phone number for VoIP, and use it through Wi-Fi.
The infrastructures in India, using circuit switch, was not seen as efficient enough for VoIP, but the issues on call drops needed to be addressed. This explains why the TRAI changed its policy concerning VoIP.