Hi tharrell,
Paul Robichaux wrote a recent commentary focusing on PhoneFactor, which you might be interested in. You can find it here. While not strictly a product review, Paul does provide some interesting insights about this product and how it works--good reading, I thought.
If you choose to implement PhoneFactor, I'd be interested to hear how it really works--come back and tell us about it!
Brian Winstead
Associate Editor