[avsteele]

So, this implies that a serious bug in any program with the 'call' hook could prevent your phone from making a call, even 911? Seems like a big deal!

In software I write, the logic for 'emergency' priority events doesn't go through the same call chain for this reason.

[xg15]

Not an Android expert, but this is how it seems to me.

It's Google's responsibility to implement the hooks in a secure way, so that an app that is registered e.g. for the "call" hook cannot prevent the call from taking place.

Seems that somewhere in there, someone messed up.

[kuschku]

The issue is that you might have a device where emergency calls have to be routed through a VoIP app, per legal requirements, e.g. if no cellular emergency calling is available (e.g. on voip-enabled wifi-only devices, or on voip-enabled devices in locations without cellular signal))