I think that it may have been sora who spoke with ven in bbs, since soras nobody (roxas) looks like ven, and it may have been mickey in kh1 but i also think that it may have been namine in kh2 talking to roxas since it was she had power over people connected with soras heart. she was the one who took away the memories of sora donald and goofy remember.
but i believe that it was sora in bbs, because the "i am a new heart" bit and hearts being wise beyond their bodies age, i.e. "xehanorts transfer in bbs". though i would agree that mickey talked to both riku and sora. because it could be that the darkness surrounding riku was deafening mickeys voice like how it blocked master arecues from contacting xehanort in bbs. so he found sora and saw the promise in him.
