It is possible to receive Wi-Fi calls from your other Apple devices, such as iPads or Macs, without a mobile network connection. To enable this, enter your iPhone Settings and tap Phone.
Tap Wi-Fi Calling. Toggle on Add Wi-Fi Calling for Other Devices. Toggle on Allow Call on Other Devices and select the device you want to make Wi-Fi calls on.
After making sure you have enabled your iPhone to allow Wi-Fi calling on other devices, enter your iPad or iPod Touch’s Settings then select FaceTime. Then toggle on Calls From iPhone.
Like above, once you’ve made sure you have enabled your iPhone to allow Wi-Fi calling on other devices, enter the FaceTime app on your Mac and select FaceTime Preferences. Then toggle on Calls from iPhone.