WiFi calling - how does it work?

[Frogger]

I have been all over the O2 site and cannot find the answers.
When a call is set up on WiFi Indios and I move out of WiFi area O2 say the call seamlessly moves to 4g.
Is this via the data capabilities of 4g or using Voice over 4g (VOLTE) which is no in my area yet. ?
Will the call transfer to normal telephony on 3G / 2G ?
In other words will the call drop when I am engaged in a call and there is no Voice over 4g locally?

I fell O2 have been economical with the facts here?

[MI5]

It will only transfer to VoLTE if your area is enabled.
If not the phone will use 3g to continue the call providing your phone switches quickly to a 3g signal.
If there is a delay in acquiring a 3g signal, the call will be dropped.

[Jeevster · Accepted solution]

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@MI5 wrote:
It will only transfer to VoLTE if your area is enabled.
If not the phone will use 3g to continue the call providing your phone switches quickly to a 3g signal.
If there is a delay in acquiring a 3g signal, the call will be dropped.

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not quite correct, WIFI calling cannot hand to 3G or 2G, only 4G, however it will have to 4G in non VoLTE coverage areas  - however once the call is ended and a new call starts, this will be carried over 3G / 2G as normal

[MI5]

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@Jeevster wrote:

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however it will have to 4G in non VoLTE coverage areas

Not sure what this means?

[Frogger]

@Jeevster. Thanks, I just tested this by disabling WiFi during a WiFi call and it continued fine on 4g data. Outside VoLTE area you cannot set up a call on 4G.

[Frogger]

‘Hand to’ I guessed

[MI5]

How can it continue on 4g if the area isn't VoLTE enabled?

[Frogger]

It is using 4g data to continue the call (rather than VoLTE) emulating a WiFi connection. ( might be WiFi assist in iOS, but I doubt it ) It definitely stays on 4g until the call is ended. Then any new calls come up on 3G.

[MI5]

Weird.

[Frogger]

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@MI5 wrote:
Weird.

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Weird but good.... trip to London next week... more tests in VoLTE area. Will update this thread then.