in two towers more than 90% of the dudes fightin are computer animated. This was done by having a list of options that each fighter could do. They dont know what the other dude they are fighting is gonna do o mcourse:D Apparently an option wasnt removed, so one guy answers his cell phone in the middle of a battle.:p

You know how those dwarves are, they like to stay in contact.

Actually for the movie makers, it becomes harder to film off the sound stage year after year. How believable is it to see a contrail in the sky when you are filming a western (for example)

the program they used for the big battles is called Motive. it makes every soldier a "living" thing, so it can make decisions for itself.

How believable is it to see a contrail in the sky when you are filming a western (for example)
So you edit it out.