In the board room scene, when the head of the board says for the fat man to call security, Loki (or Bartelby) throws a knife into the intercom. later when the "judgement" is taking place, the camera focuses on the golden idol of the cow thing and the intercom is in the picture but the knife is gone....hmmmm...
To repeat what pretty much everyone else has said, there are actually two phones. This in itself is a slip-up, because Loki says something to the effect of "I'm sorry, all lines are down at the moment." He says this, yet there's still a perfectly good phone! Sounds like a slip-up to me!
This is not a slip-up. There are two phones: one in front of Mr. Barton, and one in front of the moo-by statue. And, when Loki says, "All lines are currently down" that would not be a slip-up either. I think it is just like when one phone is off the hook in your house, none of them work. Simple explanation!
At the risk of being EXTREMELY redundant, there are 2 intercoms also when Loki says "I'm sorry, all lines are down at the moment" its for effect, I mean if he said "I'm sorry but this line is down but you can always use the intercom at the other side of the table because I only have 1 knife" that wouldn't be very exiting.