VoLTE / 4G calling not available (Sony Xperia 1ii)

[line-wait]

I recently joined O2 from Three, because Three are turning off their 3g network and I stopped being able to make any calls. I have a Sony Xperia 1ii which I believe is capable of 4G calling but this did not work on Three's network. Three has no 2G to fall back on.

On O2 I can use my phone again, because O2 are yet to turn off 3G. However, I would like to know that my phone still will, once this happens.

There are no options in my phone settings that allow me to enable/disable 4G calling.

I just spoke to O2's technical support. They told me to look through the settings which (as I already knew) revealed there was nothing I could turn on or off.

The advisor then asked me if I could access mobile internet whilst on the call with him. I could. He said this meant that my phone was already using 4G calling. I pointed out that while on the call, the symbol in the top menu bar is "H+" not 4G, suggesting the call was going through an H+ connection not a 4G one.

He assured me that no, that doesn't matter; if I can use mobile internet whilst on a call, this means my phone is using 4G calling. I was sceptical but said ok and ended the call.

However ... if I change my "Preferred network type" to "4G/5G" I am unable to make any calls.

Does this not confirm that I'm correct - my phone is not making 4G calls?

(I have tried doing the *#*#4636#*#* code and there is a switch next to "VoLTE provisioned" but it's turned off and greyed out.)

[Enlli]

Have you moved to O2 Contract or one of their PAYG offerings?

If PAYG there is no 4G calling

[line-wait]

I was initially on PAYG but have now moved to a monthly contract.

[Enlli]

Should have VoLTE available then as it's now supposed to be on by default on new contracts.

You may need to talk to O2

Guide: How to find help & contact O2 

[line-wait]

As per my first post ... I have already spoken to O2, who told me it's already working on my phone.

But I don't think it is, hence my question about whether I'm right to think it's not working.

[MI5]

You are correct @line-wait 

It isn't working.

[Enlli]

Interesting you left Three as 3G closed and you could not make calls and yet Three supports VoLTE on both PAYG

and Contract

Now you are with O2 calls are dropping to 3G when calling

Seems there may be another problem here, possibly the handset but hard to say at a distance 

[line-wait]

Thanks @MI5 .

@Enllithat's right - VoLTE didn't work on Three either (even though the handset is a 4g/5g one).

From what I understand, VoLTE has to be enabled at the provider end as well as on the handset.

My handset, the Sony Xperia 1ii is one that was sold by O2 (even though that's not where I originally bought mine).

[MI5]

@line-wait 

O2 tell us that 4g and wifi calling is on by default now for all supported phones and contracts.

Check your firmware is fully up to date, but the age of the phone might be the issue.

[Enlli]

As stated by @MI5 VoLTE should be on by default. It should also have been on by default on Three. As the phone has worked on neither I suspect handset/ Firmware problem.

Is it possible to put the SIM in a from a borrowed phone that has VoLTE and see what happens.

It might also be useful to put your SIM in the borrowed phone