The truth is I don't actually listen to a lot of music but I do listen to Audiobooks a lot on my phone. Either way I've found it extremely inconvenient to have headphones with me everywhere I go and even when I have them the cords always get in the way. For the last 3+ years I've been looking for a good Android solution to send the audio to my Bluetooth headset.
Up until recently every app that purported to do this just didn't work for me. Most of the app developers make a clear disclaimer that their apps will only work with certain handsets and I guess up to this point I had the wrong phones or wrong apps. Recently I decided to give it another try and so I downloaded about 7 apps before finding one that worked correctly with my HTC Rezound.
Let me introduce you to BTmono. BTmono has a free and a premium version of their app. This is really important so that you can test the free app so make sure it will work with your phone before paying for the app. The premium app is only $1.
It does what it says really well. You must first have Bluetooth turned on and your device paired. Then open the app and turn it on. There are several features that are reserved for the premium app including the awesome widget. Also, only with the premium app will the app resume working after being interrupted by a phone call.
You can adjust media volume directly via the app interface but I'm perfectly accustomed to using the hard keys on the side of my phone.
Although I haven't tried it myself, the developer warns users that if you want to use this with Skype you need to first start your Skype call and then turn on BTmono.