And CDR and LUD. Call Data Records (numbers, time, duration) and Local Usage Detail (they use "LUDs" on TV)

Not serving subpoenas, responding to them. Police subpoena stuff like "everyone who was within x feet of this phone number or location between these times" and the telcos can't just say "we don't keep that data."

Subpoenas are based on information you have. Where is the law or regulation that says they need to keep it?

Telcos keep it because it helps them with network capacity planning and is incredibility financially lucrative when they want to sell the data. It's probably more to fill in their data product for malls and fine grained location than to do it for subpoenas, which if they had a choice would probably rather not have to do.

…why not? Is there a federal law compelling then to record and store precise location data indefinitely?

I'm not sure if it's a legal requirement or they just don't want to upset law enforcement. All I know is they're using our data warehouse and having me write queries that answer those subpoenas when they come in.

Well I know that in the UK it is a legal requirement, but not sure about the US.

> the telcos can't just say "we don't keep that data."

Not sure what country you are in, though that is untrue in USA. Even if they have the data a USA attorney can try to argue that the request is unduly burdensome or too broad and ask court to quash subpoena.