In iOS 5 the lock screen can access the camera app.
Is there a way to change the default app that is launched. I would rather use instagram for its social media connections and filters.
Sorry, but Apple doesn't allow this, and it doesn't even look like there is a jailbreak tweak for this.
If you are runnning a jailbroken iOS5 device, AnyLockApp seems to be able to change the default app.
You will have to enter your passcode in order to use the app though.