I have been trying to catch my grey saying hello on video now for about a week. He seems to only talk when I'm busy doing something, its a bit noisy, or if I'm walking away. Well today while cleaning his cage I got him. Not the clearest hello but he's only 3 months and 6 days old. You may have to turn up your volume a bit and listen for it @ the 5 second mark.
Youtube: http://www.youtube.com/watch?v=VJ4kGKMd71w
or
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