This seems like the same problem others are experiencing, e.g.
https://community.idmobile.co.uk/ask-a-question-18/unable-to-make-id-mobile-calls-61529
I have a good 4G signal and 4G calling is enabled on my phone (a OnePlus 5T with Android 11). It works on my other (EE) SIM.
In areas where only an LTE signal is available, I am unable to make or receive phone calls on iD. Where 3G or GSM are available it works fine. Where both are available I can reproduce the issue by forcing the phone to LTE only in the settings.
I have gone through support - reset network settings, manually force network to iD, clean SIM etc. with no success. They are sending me a replacement SIM but I would be surprised if that helps.
If there’s any more debugging info that would be useful I can provide it.
Obviously I cannot remain as a customer if it’s impossible to make voice calls in large areas of the country.
