VoIP enables the delivery of voice communications over IP networks, such as the Internet. Whereas, PSTN is an aggregate of circuit-switched telephone networks that are operated by national, regional or local telephony operators.
Cloud telephony is generally associated with VoIP however, MyOperator uses only PSTN networks for its Indian customers due to legal constraints.
When a customer calls on your business number, the incoming call lands on the server (IVR). As soon as the customer chooses a department from the IVR, another call is generated that connects the caller to a specific agent. This is done through PSTN network.