My scenario (which is slightly different but this is a solution for all!)
Lock button not working. Can't lock screen or take snapshots.
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Try going into settings and choosing assistive touch. You can move the little circle anywhere on your phone (I chose between the time and battery since it doesn't interfere with anything)
I got water damage in my iPhone 4 and the lock button stopped working. My roommate who has an iPhone has seen a similar problem with the lock button.
Turned that on. And voila!
Explore it and you see many options, some I don't care to delve in to, but now I know how to take screen shots and I only need to use one finger now XD
Also, no repair, no expense, already built in!