The requests are so numerous, in fact, that Apple has had to create a waiting list. As an example, ATF agent Rob Maynard tried -- for nearly three months last summer -- "to locate a local, state, or federal law enforcement agency with the forensic capabilities to unlock" an iPhone 4S. He failed.
Eventually, he turned to Apple. While the Cupertino, Calif.-based firm said it could unlock the phone, it said that because of the waiting list, it would be about seven weeks before they could address his needs. In total, it appears the task took Maynard at least four months, including his attempts with other agencies.
While there are some third-party software packages that claim to be able to decrypt and extra information from iOS devices, they often cannot recover all of the information on the smartphone, and they sometimes don't support the latest hardware or iOS versions.
For example, Elcomsoft's iOS Forensic Toolkit only supports iOS versions 3, 4, and 5, at this time. Meanwhile, the Oxygen Forensics Suite 2013 does support all current devices, but adds that "password-protected devices will require password to perform data extraction."
Not having the password would seem to be a common issue with these sorts of seized iDevices, so we're not sure exactly how good Oxygen Forensics' service is.
Prior court rulings seem to have decided that a suspect cannot be forced to give up the encryption key or password for their hard drive or other device, unless the "foregone conclusion doctrine" is in play.