It should just be using the native wifi calling feature within android as per the Galaxy S8 and S8+
There is no need for any specific O2 firmware but a good point raised nonetheless.
Maybe
@Chris_K could let us know ?
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)