Yes I definately think they talk, to us and eachother. Jack definately talks to me all the time, and I talk to him. I tell him what I'm doing when he's with me and he stays with me while I'm doing chores and talks back at me.
When Kevin comes home from work, and he goes up stairs to get changed Sunny talks to him, and it's so loud I can hear it downstairs! She meow and meows at him, and I'm sure she's telling him she's missed him and about her day.
And like Sandra said, about the birds, how else would they know?!
And with our ferals, at first we only had one, and then we had three grown up cats, before the kittens came along.
I'm sure they told eachother that there was this house where there were nice people who fed them!