How else can they do it? As I understand with android they have to list themselves as a dialer to make and receive calls.

Not trying to defend the programming screwup. Just the idea that they can magically send and receive 911 calls without being interfaced somehow with the dialer.

Can't the app have an internal dialler? They have their own iOS. I seem to remember Whatsapp on Android had this, but it was a long time ago, and I may be mistaken.

Under the hood I would expect it to still be hooked into the dialer system api that google exposes. Likely this was where the undefined behavior showed up.

Android allows VOIP apps to register as a dialer. They have allowed this for YEARS. One company I worked with some years back was looking at working with phone vendors who based their phones on Android about replacing the default dialer. It didn't happen, but it was an option even a decade ago.

The programming screwup? Yes, that is a Teams thing.

I personally wonder if this situation gets even goofier with Work/Personal profiles on Android. It's not something I have looked into. I have a Pixel 5 as my "work" phone and it has the profiles. But I rarely use it for anything but messsaging/Teams meetings/etc.