Samsung Gleam SCH-U700 / Muse

Someone said they figured out how to lock the front keys but didn't say how they figured it out. I didn't even know they would lock until last week when I saw the little lock symbol up there and the keys were locked...thank God. But then I had to turn off my phone and turn it back on and they are unlocked.

I have no idea how I managed to lock them in the first place so don't know how to do it again.

Please help!!!