A. What constitutes an "unusual" inclination? What if you want to use the device while lying on your bed? I do this a lot. Phones are routinely used in many different positions. This lock would only work if the phone is carried in a position that is not "usual."

B. Sensing an object in front of the display will require a sensor that will add weight, bulk and cost. I'm not sure it would be worth it for something not very necessary.

C. How does the phone know that it is not dark because it's night or you're in a dark room?

D. has the same problem as B. I'm not too sure if an electric field hand sensor is all that feasible in a phone.

It appears that you want to introduce a keypad lock to prevent the keys being accidentally activated while the phone is in your bag or pocket. That would be a great idea, but you should decide which method is best and stick with that. There's no reason to clutter the device with more locking features than necessary to accomplish the job. It would be a real nuisance if the keypad locks for reasons that the user is unaware of while they're trying to use it.

Still, a keypad lock would be great. Just make sure the system is a well chosen one.

Two words

Apple iPhone.

It (supposedly) has many of those innovations.