Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
That's in your local system.If my iPhone is on, it rings or if unanswered, it goes to voicemail. If I'm out of a service area, the phone's incoming call gets a message (I don't recall the message) after several rings and if it's powered off, it goes straight to voicemail.
Aren't these "glass" cockpits designed that even if there were still a total electrical failure or computer crash; a few vital instruments will still operate because they are analog in design?