There was a long debate over this point some years ago here on the GBB. Many assumed it was Tessio who spoke that line simply because he was the one holding the vest. And it is amazing how many members noticed small details that most others may not have picked up on.

You got that right. When I re-watched the scene,and listened to the voice,it couldn't have been more clear that it was Clemenza. I guess when the package is shown,our attention is drawn more to the visual impact.