Here is Apple's current statement: Apple - Privacy - Government Information Requests
On devices running iOS 8, your personal data such as photos, messages (including attachments), email, contacts, call history, iTunes content, notes, and reminders is placed under the protection of your passcode. Unlike our competitors, Apple cannot bypass your passcode and therefore cannot access this data. So it's not technically feasible for us to respond to government warrants for the extraction of this data from devices in their possession running iOS 8.Reading the statement (not just the paragraph above) in its entirety, my impression is that Apple would, if it could, and if the warrant called for it.
On further searching .. Apple slaps a passcode lock on iOS 8 devices, but cops can still inhale your iCloud - UK Register: 23 Sep 2014
This article purports to quote from Apple's previous privacy remarks:
Apple can perform this data extraction process on iOS devices running iOS 4 or more recent versions of iOS. Please note the only categories of user generated active files that can be provided to law enforcement, pursuant to a valid search warrant, are: SMS, photos, videos, contacts, audio recording, and call history. Apple cannot provide: email, calendar entries, or any third-party App data.FWIW, that article is pretty informative.
Apple has replaced the "previous privacy remarks" with the new sweeping statement that ALL data uploaded from customers' devices with passcodes are "already encrypted before Apple receives it." It is then anonymized and then broken into smaller packets, additionally 256 bit encrypted again, where it is stored for retrieval only by its owner. Even Apple cannot decrypt it to useable form. "Cops can still inhale your iCloud" but all they will get is undecypherable mixed up gobble-de-gook without your key that may be mixed with other users data encrypted with other keys.
Note that "call history" and "third-party app" data can be subpoenaed from carriers and the providers of the third-party app publishers, assuming the app uploads anything to the app's servers. Apple cannot prevent the authorities getting that.