I'm fairly sure that he has done this before, but today we saw Miles roll from him back to his tummy for the first time. He started completely rolling over (360 degree rolls) to move himself from one location to another. Jason would put his blocks a few feet away, and he rolled over to them.
I have noticed him rolling onto his side a lot in his crib during his naptimes. I suspect that he may also be rolling onto his tummy as well, but he always sleeps on his back.
I think we may have a crawler in our near future! He is learning fast!