SPFX Tab for calling (aka calling extension)

[petrp314]

Hello,
I have tried to create an SPFX tab as calling extension, described here: https://learn.microsoft.com/en-us/microsoftteams/platform/apps-in-teams-meetings/build-tabs-for-calling

It works for PSTN incoming calls, the tab is visible and works. I can get the calling phone number just fine.

However we have tried VOIP calls and the extension is not present in such calls. Is there any official guidance where and how the calling extension works and where not?

I have only found one sentence at the beginning of the mentional link: "You can now create personal scope apps that integrate seamlessly with Public Switched Telephone Network (PSTN) and Teams-to-Teams calls."

Is there more details somewhere? Is VOIP supported for calling extension SPFX solutions?

Maybe @VesaJuvonen can point me to the right direction? Thanks a lot. PetrP MSFT