[gruez]

> So it's not the most quiet attack. But people replace their phones and forget account details so it may pass unnoticed by some of your contacts, particularly if you have no other channel to reach your contacts.

So in other words, such attacks aren't viable for dragnet surveillance and must be targeted. But if you have reason to believe that you'll be targeted by the government for surveillance, you'd be on the lookout for signs like "your safety number has changed"?