I discovered a bug with my iphone over the weekend. Due to an update, when using it with Bluetooth, I found that while I could make and receive calls, my voice mail showed up but I couldn’t hear it. AT&T blamed Apple and vice versa. Finally, we discovered that it was sort of sending the sound to Bluetooth, but not really.
We reset everything, including clearing all my voice mail. Nothing worked.
All I had to do (which is a bit of a pain in the neck) is route the audio to the handset manually and …fixed.