I just did this on a locked iPhone i Found Yesterday to try to identify the owner.
It was locked from too many bad PIN's entered and I was able to access Photos, Call Log, TXT Messages, etc.
Didn't give me access to every single thing on the phone, but that is still a lot considering this is a shareware limited app anyone can download.
There are more advanced Forensic programs that are available, but they can get more pricey.
But if anyone with google can find a shareware app, what hope to you have against the government with all their money and resources.