I'm not sure if I've seen cats learn actual words, but I haven't had many cats either. There is definitely communication through tone and visual signals though. Every night I wait for Jasper at the living room door, say "come on" and he (usually) follows me up the other end of the house. If he is up on a bench or somewhere he shouldn't be, he very quickly jumps off if I say "get down", "off" etc but I think that's tone and saying words sharply. I think we probably communicate in ways that I'm not even really aware of, like making room for him on my lap in response to a look or gesture from him. My favourite at the moment is when he jumps up on the table, then he beckons me over and gets all smoochy. I'm just hoping he will learn what "No, I don't want to sniff your butt" means