Voice Over WiFi is the term used by operators who refer to the provision of telephony services over a WiFi access. From the user's perspective, the experience is similar to VoLTE, or traditional voice calls. However, from the network perspective, it is quite different, since the WiFi network is not an integrated part of the mobile network. Voice over Internet Protocol is a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls by sending voice data in packets using IP rather than by traditional circuit transmissions of the PSTN. The quality of the call can be poorer, and in general is similar to that of over-the-top (OTT) applications.
See VoLTE