From Threat Level:

The carriers said they responded to police emergencies, subpoenas and other court orders. They did not clearly say how many times they responded to probable-cause warrants. That’s because much of Americans’ mobile-phone data is not protected by the Fourth Amendment.

The reports showed that AT&T, the nation’s second largest carrier, received about 125,000 requests from the authorities in 2007 — mushrooming to more than 260,000 last year.

Verizon, the nation’s largest carrier… said it also received about 260,000 requests last year…

Sprint said it has received…500,000 requests last year.

…T-Mobile, declined to divulge how many requests it gets.

McCone said the company (AT&T) employs more than 100 full-time staffers and “operates on a 24/7 basis for the purpose of meeting law enforcement demands.”