Interesting New York Times article: "Deciphering the Chatter of Monkeys and Chimps." Excerpt:
It is tempting to think of the vervet calls as words for "leopard," "snake" or "eagle," but that is not really so. The vervets do not combine the calls with other sounds to make new meanings. They do not modulate them, so far as is known, to convey that a leopard is 10, or 100, feet away. Their alarm calls seem less like words and more like a person saying "Ouch!"—a vocal representation of an inner mental state rather than an attempt to convey exact information.
But the calls do have specific meaning.