If you can get the inside panel off - pull on the metal bar that runs back to the lock. If you pull off the panel, there should be a stub sticking out of where the inside handle connects to. The stub and the device bolted to the door (called a relay, if you care) hook to this metal bar. If you are lucky, the relay is the problem and pulling on the bar will open it. IF you aren't the lock itself is jammed. Unfortunately the screws holding the lock on are only accessible when the door is open. I suggest you douse the lock several times with WD-40 or your favorite penetrating oil, then pull hard on that relay bar. There is a chance that the lock mechanism is jammed on the receiver portion on the door jamb - in this case the best thing to do is to hit the door with your shoulder from the inside - it should eventually open up.