S10+ VOLTE Option Keeps Going Grey on O2 after 24hrs

[Members_ARy5juP]

I bought my excellent S10+  (runs on OXM firmware / Android 11), but every 24hrs the VOLTE option keeps going grey (preventing me from selecting it), and the WIFI calling option vanishes.  Rebooting brings them back straight away

I am now in back and forward ping pong between O2 and Samsung.  Some O2 agents tell me OXM wont work (and has to be O2 firmware), others  (and indeed their own website) tell me it will, Samsung tell me its not their issue, but reading some of the forums its a known fault that Samsung wont admit it??? I am now lost in this mess.   Its taught me a valuable  lesson to never buy direct SIM free phones!

Before it is suggested, I have factory reset, network setting reset, swapped sim, updated all software, cleaned the SIM,  cleared the cache, virus checked...      I cant be the only one with this issue? - Please can someone help before I lose the will to live.

[Pugs1957]

The O2 agents were correct. If you want wifi calling you need O2U as your CSC.

[Members_ARy5juP]

Some agents were telling it open market firmware does work, and their own website says it should  (ie no "*" next to the model on the list.  Defeats getting SIM free phones if the operators reserve the best services for phones bought through them.   I assume if I bought a PAYG O2 phone that would be one way round in future - then SIM swap?  I am on great O2 deal so want to stay on my current contract.

[ynneL]

It used to happen to my girlfriend's unlocked Note 10 all the time it happens when the phone is restarted and it unregisters from the IMS the way I found to fix it was turn your device on aeroplane mode and restart it once it's started then turn aeroplane mode off it must be something to do with O2 because she's on EE now and never has any issues anymore