I would suggest using the mute/standby button instead of the keypad lock. I use the keypad lock for a long time, but in the end didn't like it as much.
With using the standby, the only way it'll come out is if you press the standby button again. The only issue I see with that is I still think if you move right it'll answer the call without you knowing, I'm not sure on that one though. Maybe try it for a few days and see what happens?
-"cuentale que te traigo loca"-