What if they purchase the information from a company peddling it rather than compelling cell phone companies to hand it over?

This data was being “compelled” from Google. If Google had told its users that their data might be sold, had sold it, and the government had acquired it that way, this case comes out differently.

In reality, Google simply stopped collecting this data in their cloud, leaving it only on the phone.

Highly recommend (as always) listening to the oral arguments in your favorite podcast player. The specific question of how Google’s T&C’s mattered here came up more than once.

For an example of what can be done with such purchased data, one project at a previous employer was:

- identifying all cell phone #s which would regularly appear w/in a certain radius of any State Police Barracks

- disambiguating that from people who lived/worked nearby and/or who met certain criteria

- determining the income and certain other criteria of the remaining numbers

- identifying the home address of the remaining cell #s which met the final criteria and mailing a franchise offer to those cell #s with the assumption that it would be targeting State Police Troopers

That is the loop hole IMO and that's how they will get around it.