I use voice to text for text messages and email all the time. I've noticed it has been horrid with the S4 compared to the last couple HTC phones I've had. I think I've got it figured out though, but I'd like someone else to confirm... go into call settings and turn off the option for background noise. It's like a night and day difference for me. I called someone with the setting on and off and they said I sounded clearly different/better with the setting on. Too bad... voice to text has GOT to work!