> I want Signal, Slack, Teams, my apartment buildings intercom system, etc, to be able to present their own native incoming calls through the same dialogs that regular calls come through. But not at the cost of potentially not being able to call emergency services...

Understand that calling emergency services on VoLTE is essentialy VoIP as well - noone here disagrees that this is a horrifying bug. But the issue with this bug is not the APIs that allows VoIP apps to integrate into call system (after all, those APIs also make Signal/WhatsApp/Skype/Teams calls work over systems like smartwatches, Android Auto and Bluetooth car integrations) but the fact that Android somehow missed the fact that a buggy app can stop a call.

Agree completely.

Incoming calls or manually dialling a number directly through the respective app is a different matter, but when you click a stored number in your contacts list, or a phone link in your browser or another app, or anything like that, that app just hands the number to the OS and basically says "please call this number for me".

If you want to allow alternative VOIP apps and things like that to exist, at that point the OS must allow routing that number to any app that claims it can handle (outgoing) phone calls.

Yeah sure, and for most things it's fine if things break, irritating and bad press, but fine. Things like calling emergency services can never be allowed to break. It must have fallbacks, if it even needs to be allowed to be overridden in the first place.

According to this old bit of documentation (https://android-developers.googleblog.com/2013/05/handling-p...), the usual way of intercepting call requests should already handle emergency calls ("Note that the system broadcasts NEW_OUTGOING_CALL only for numbers that are not associated with core dialing capabilities such as emergency numbers."), so it'd be interesting to know what went wrong in this case (and why only on Android 10 and newer), but until then it's hard to say more and it's all just speculation…

There are many reasons why an app would want to be notified of a call taking place - e.g., a music app could use this event to auto-pause playback, Teams might set the availability status to "busy", etc.

The question is what should happen if such an app takes an excessively long time handling the event. In this case, the OS should not wait for the app and should directly go on making the call. The bug seems to be that the OS did wait, so a misbehaving app can effectively block phone calls by e.g. going into an infinite loop.