Can I unlock my iOS, or access it's data some way, via PC? In other words, if my iOS device is stolen, will the person be able to get my data by pluging it in a PC and use some trick (or by being able to jailbreak my device while it is protected with a passcode lock)?

For the discussion, please assume my iOS device:


is in airplane mode, so I can't remote wipe.
not currently jailbroken
In general, no. iOS devices where you have enabled hardware data protection on iOS 4 or later require the correct passcode to be entered. If you haven't enabled a passcode, the data on the phone is easily available to the thief assuming they have either minimal training and/or money.

So, as long as they can't guess the passcode from looking at smudges in the glass or recording your motions before the device is stolen - you are as secure as the passcode you have chosen. Most times when the government needs to bypass the passcode locks, they get a warrant for your home computer and take the key that iTunes uses to unlock the device and use specialized software to send that key.

Once someone is willing to spend thousands of dollars on either specialized hardware and software or thousands of dollars to hire someone trained in iPhone forensics to do the work, the chances of "cracking" into the device are higher, but still not assured if you have chosen a good passcode and not allowed your keys to be stolen by a backup to iCloud or let the thief get to your computer as well.