Phone calls over the LTE cellular data network. Voice over LTE (VoLTE) is a voice over IP (VoIP) service that uses the same IP network architecture as LTE data. Although transmitted in IP packets the same as data, if cellular data in the device is turned off, phone calls can still be made.
Many LTE initial deployments continued to use the existing 3G networks for phone calls. It took time for the carriers to build new infrastructure across the country so they could switch from 3G voice to LTE voice. Phones may include a "Turn on/off VoLTE" setting to accommodate regional differences. See LTE
and cellular data