Friend is a lawyer. About 9 months ago, he got a call from a detective asking if he could come by and see him. "Which of my clients is it about?" Detective said he couldn't say, but needed to come by anyway, and asks if he can be at lawyer's office in 30 mins. Detective shows up with other law enforcement- I think it was a Texas Ranger. They were there not to ask about any of his clients, but him. The investigation of a murder about 45 mins away had gone cold, but prosecutors got the judge to order cell providers to identify everyone whose cell pinged a tower or towers near the scene during a several hour time frame before and after the murder. Turns out he was passing through the area on his way to a rodeo. He had nothing to hide, but said it was still unnerving as hell to be questioned in a murder case. So yes, with a court order in Texas, the cops can get that info. The murder happened in a smaller community, so I doubt there were thousands of pings to look into.
I'm not a criminal lawyer, but I know defense lawyers have raised the issue of whether customers have any reasonable expectation of privacy regarding their cell phone data.