Solved! Go to Solution.
Thanks for posting back. I’m afraid that Handset isn’t officially supported by BT mobile for Wi-fi or 4G calling.
Some Pixel users have reflashed their firmware to try and get it working with a mixed result.
All BT sims are provisioned for the service, but currently only the S8/S9 and iPhone 5s and above are supported.
You can read more about Wi-fi calling and 4G calling using the link below. If you are trying to improve indoor coverage. You can use a BT signal assist box.