No such button. [edit]That I know of at least.[/edit]

If you're that determined to destroy it (I can understand this), then yes, soaking it in water, then smashing in with a hammer (probably way more efficient than driving a car over it) should make it perfectly inoperable.

I suggest you disassemble the device and perform the above on just the motherboard - the keyboard, screen parts, perhaps just the frame in general, definitely the battery, are all things that may well be useful to someone in the community, and certainly have no useful data from the phone on/in them.