Voice activated text messaging like Droid X

I just purchased my iPhone 4 after using a Blackberry for a few years. I love the phone but found that my son's Droid X has a nice feature that allows him to open his text message function and simply press a microphone icon and begin speaking his text message. It works either when composing a new message as well as when replying to a message from someone else. I don't see that function on the iPhone.

I purchased Voice Text Pro but it doesn't seem to integrate with the iPhone's message center. My son sent me a text message but I coun't use Voice Text Pro to reply.

Anyone have any suggestions? Thanks!