Got a wireless headset a few months ago and discovered that it would read incoming SMS messages to me. It would neatly interrupt a podcast currently in progress, read the message, then go away again and resume playing the podcast. I didn't know it was going to do this but, hey, it was neat.
It suddenly stopped doing this a week ago. Now I'm finding I miss this feature.
I've restarted phone and headset. I've also made sure that in Settings->Speech-> the "Play audio confirmations" option is set to **On and "Read incoming text messages aloud" is set to Bluetooth (also tried changing this to Bluetooth & headsets).
This is WP7.5 on the Titan and a Plantronic M50. Although, none of that should matter much because it was working just fine until, as a I say, a week ago.