You mean audio chat? there is no way while playing dark souls. You can do audio chat while no game is on in the background, and in select games that offer the option, its in the very last icon I believe its a headset over a keyboard.
If you need to audio chat in dark souls I'd recommend a computer program like skype or something similar.
I don't think you can run skype off your ps3, you'll have to have a laptop or smartphone I think. Just install it and friend the person you want to chat with, I am sure you could get invited to he forum chat there too if you asked around.
i also hate hearing people talking when playing but not if i'm playing with a friend him talking i don't mind but when i play and other players i don't know are just going nuts all talking at the same time and screaming, that is just annoying and distracting as hell
I think FROM intentionally left out voice chat because this is meant to be a lonely journey, even when you have summoned phantoms. I rather like not having voice chat, though I have to admit I have never played a game with voice chat before. Demon's Souls was the same way. I'm not sure the game would have the same ambiance if I had kids (that should not be playing the game in the first place) screaming in my ear after I have invaded and off'd their characters.