iPhone 4s screen goes black

The title pretty much says it all. The screen goes black when I'm using the talk to text feature. I am currently using the phone in landscape over Wi-Fi and when I speak my message, the screen goes black and I hear the chirp indicating that my message is done (even though I'm still talking). After a moment, the screen comes back and my message posts (albeit incorrect). This has been happening consistently during this entire texting conversation and has also occured in the past.