Thing you'll need
-Internet Connection on iPhone
For this Instructable you MUST HAVE A JAILBROKEN iPHONE!!! If you don't, this process won't work for you. If you don't have a jailbroken iPhone, check out the Instructable I made that tells you how to jailbreak it.
Step 1: Download Some Files
The first thing your going to want to do is go to Cydia. After it loads, search "Bluetooth Mono SBSettings Toggle." Open the link to the package and install it. It should install the Bluetooth Mono SBSettings Toggle along two other packages, one called SBSettings (The program that shows the toggles) and the other called Activator (The program that allows you to open SBSettings).
Step 2: Open SBSettings
After the files have installed and your phone has restarted, go to settings. Go to the Activator settings and select an activation method. After you have set one, use the activation method you have chosen to activate SBSettings. In SBSettings you will see a toggle like the one in the picture below (The icon on the second row that says Bluetooth).(Note: even though it looks as if there is two of the same toggle buttons, one is for turning Bluetooth on and off while the other is for turning the sound and music redirection on and off). Now make sure that both of these toggles are turned on.
Step 3: Connect Bluetooth
Now all you have to do is connect you Bluetooth headset and start listening to some music. Also, with this toggle on you can still use your Bluetooth to make phone calls. If something doesn't work for you or if you have any sort of suggestions or feedback, leave a comment about it and I'll try to reply.