VoLTE on OnePlus 5

[Anonymous]

Well I been told by your customer service that O2 supports VoLTE and so does the OnePlus 5. If that's the case why do I not have a VoLTE option appear on my phone like other people's on different networks?

Someone else on XDA that works at O2 said that it does not support VoLTE so I'm confused.

As you can see in the screenshot below they have an option and I do not. 

I even tried enabling it manually via phone information menu (advanced) but it just turns back off every time i come off it.

I also come accross this post on XDA Developrts. 

VoLTE does not work by default. Special configurations are needed for each provider. If the VoLTE works for some provider, then it does not guarantee it for other providers.

Please could someone with device, copy+zip+upload files from their Op5. This would help determine which providers have VoLTE configurations available.
Use some advanced file manager, to find files with extension .mbn
These are usually in 
either /system/etc/customization/modem/
or /system/etc/firmware/
or /system/rfs/apq/gnss/readonly/firmware/image/modem_pr/mcfg/configs/mcfg_sw/generic/sea/

Ok, i have managed to get files from phone that was on display in shop with help from finnish friend.
Following special configurations are available, pointing to some providers having VoLTE.

mcfg_sw/generic/apac/reliance/commerci/mcfg_sw.mbn
mcfg_sw/generic/china/cmcc/commerci/volte_op/mcfg_sw.mbn
mcfg_sw/generic/china/ct/commerci/openmkt/mcfg_sw.mbn
mcfg_sw/generic/china/cu/commerci/openmkt/mcfg_sw.mbn
mcfg_sw/generic/eu/ee/commerci/mcfg_sw.mbn
mcfg_sw/generic/eu/h3g/commerci/uk/mcfg_sw.mbn
mcfg_sw/generic/eu/telefoni/volte/uk/mcfg_sw.mbn
mcfg_sw/generic/na/att/volte/mcfg_sw.mbn
mcfg_sw/generic/na/tmo/commerci/mcfg_sw.mbn
mcfg_sw/generic/oem/lab/volte_te/mcfg_sw.mbn
mcfg_sw/generic/oem/oversea/commerci/mcfg_sw.mbn
mcfg_sw/generic/sea/ytl/gen_3gpp/mcfg_sw.mbn
mcfg_sw/generic/common/row/gen_3gpp/mcfg_sw.mbn

As you can see there is an entry saying 

mcfg_sw/generic/eu/telefoni/volte/uk/mcfg_sw.mbn

This one looks like O2 to me by the name "telefoni" which I guess means Telefonica.

So you guys support VoLTE and looks like the phone supports it through O2 too so why do I not have the option? 

but accoring to OnePlus customer service only EE supports it on the OnePlus 5 in the UK. Which I find absoletely ridiclous considering the phone is sold exclusively through O2 but yet O2 doesn't have VoLTE on OP5 but EE does and they don't even sell the phone!!

"OnePlus 5 hardware circuit can totally support for VoLTE, but VoLTE service also needs carrier support. Now only followed carrier could support VoLTE service: 

Completed
VoLTE:
China: CMCC
UK: EE
US: TMO
Inida: RJIO

VoWiFi:
UK: EE
US: TMO 
More and more carrier will support for VoLTE soon."

Sort it out O2

[MI5]

That phone is not supported yet.