Hi @Nicholas_829036 ๐
When we talk about 'unlocked' phones this only covers the use of a SIM from different suppliers.
Does your phone have the ability to make VoLTE call and connect to WiFi Calling? Are these options available options on the handset? In the Settings under Connections/Mobile Networks/Network Mode do you see '4G' or 'LTE'?
You need the 'LTE' option available to be able to use the VoLTE connection and to make/receive calls.
What a lot of people dont know is that the phones software, and its updates, are controlled by the original network the handset was sold by.
What you need to do is look for the 'Software Information' that is on your phone. If it has any of these codes in it then that means the phone was originally sold by Vodafone and they will control the necessary updates to the software that enables VoLTE and Wifi Calling.
Codes:- TSC, VIR, VOD (Vodafone)
If you see any of these codes then that is why your partners SIM works and yours doesn't.
A good idea, to see if this is the case, is to put your partners SIM back into your phone and perform a 'Software Update' as this may then get the relevant download to enable the LTE connection.
I did a post with regards to this:-
https://community.smarty.co.uk/t5/chats-hacks/can-t-make-receive-calls-not-necessarily-a-network-pro...
Good luck!
