I use another feature for sms on my 820. If you go into:
Settings
Speech
Turn 'read incoming text messages aloud' to 'always on'.
This means when you receive a text, it tells you who it is from, without having to do anything. The phone then prompts you as to what you want to do next, e.g read it or ignore.
If you say read it, you then have more options, e.g reply and a few others.
I'm a painter and I can be up a ladder, say read it and reply whilst still decorating. The phone sits in a pouch off my belt and most times it works fine, occasionally though it does mis-interpret the odd word or two which can be funny.
I wish there was a solution for email as well though!
Hope this helps,