FWIW: At 911, we were the police, organizationally. Actual sworn cops didn’t have special access to phone companies that dispatchers didn’t— we’d probably be the ones making the request for them if it was that urgent. (In some places dispatchers are cops, but is very uncommon, and the distinction isn’t important in this respect.) Phone companies aren’t going to hire a bunch of specialized workers to comply with legal orders instantly instead of soon enough. And there surely needs to be a ticket made and such… it’s not like CS reps have that info.

The NSA doesn’t need warrants in many cases because they can get the information they need from the government’s own databases. I’m not an expert, but as far as I know, if they need someone’s location from a phone company they do need a warrant or to prove there were exigent circumstances, which is why they just get shit from data brokers. Some politicians want to close that loop hole but most either don’t, or don’t care enough. Some, shockingly, even want to reform FISA.

The NSA doesn't need warrants because breaking federal law is easier to get away with when you have one of secrecy, some relation to security, presence in the meetings where you'd be discussed, and largeness (which provokes acceptance), and they have all four.