Jake Whitaker The voice is probably Michael's dad. How else could Michael and his mom been living off the grid for so long?
John C I think that the voice is one of the four 'dead' glows. We know that Hatch was lying about one of them being dead, so wouldn't it make sense for Hatch to be lying about the others. If you disagree with me about Hatch lying about at least one of the glows, then you weren't paying attention to the last part of the book. (hint: GLOW who used something ELECTRICAL in the body to paralyze.
Vivek I think it is Dr.Coonradt because at the end Schema recognized the voice immediately. He wouldn't have recognized someone as minor as Michael's dad