Being that soda is a nickname for carbonic acid, and used in everything containing carbonic acid, that can be used. Pop is actually used as a nickname for the phosphates within the soft beverage, so "pop" can be used. Coke comes from the coca plant which the taste is derived from, and later for cocaine. So I guess calling any soft beverage using the coca plant "coke" would also be correct.
That being said though, I call them what they call themselves in the Wall Street Journal... SODA Companies.