FaceTime is Apple's proprietary VoIP service that enables users to make video and voice calls over the internet. While it's commonly associated with Wi-Fi usage, FaceTime can also operate without a Wi-Fi connection by utilizing your cellular data network.
Using FaceTime with a Cellular Network
Step 1: Ensure that your mobile or cellular data is turned on. For iPhone X or newer models, swipe down from the top-right corner of the screen to open the Control Center. For older models, swipe up from the bottom of the screen. Tap the 'Mobile Data' icon to activate it; the icon will appear