Sony Xperia 10
It's not possible to use Wi-Fi calling
Solution 2 of 4: Your phone needs to be restarted
If your phone is slow or freezes, it might help to restart it.
Step 1 of 2
Press and hold On/Off.
Step 2 of 2
Simultaneously press and hold the upper part of the Volume key and keep them both pressed until your phone restarts.