Not possible to block VoIP calls in iOS 13?

Question

CallKit's call directory extension can be used to block standard phone calls. However how is blocking a VoIP call supposed to work with iOS 13?

When there is a VoIP call your app receives a VoIP push, but now with iOS 13 Apple are mandating that when the push is received the app must call CXProvider.reportNewIncomingCall().

However when reportNewIncomingCall() is called, the OS displays an incoming call screen (which is not the same as for a regular incoming call). It is apparently not possible for this call screen to be suppressed, and even if reportNewIncomminCall() is invoked with a parameter which is a number which has been registered as blocked with the CallKit extension, the call screens still being displayed.

So it would seem it is impossible for an application to offer the ability to block a VoIP phone call (unless the app sends its list of blocked numbers to the server, and the server doesn't send the push for a particular handset for blocked numbers. But if the app is installed in hundreds of thousands or millions of handsets, that's a large undertaking on the server side to implement).

Answer 1

I had some correspondence with an Apple Voip engineer. Apple are expectingthat if you need to block Voip calls then you need to do it on the server, not the handset.