As far as I can tell, that's a yes to both: Signal supports VoIP calls, they're definitely using the PushKit VoIP API, and I assume they're using that API for b

As far as I can tell, that's a yes to both: Signal supports VoIP calls, they're definitely using the PushKit VoIP API, and I assume they're using that API for both text notifications and calls since the code doesn't have any reference to the other API they could use.