Headset for voice when using car adapter

[necigrad]

I have a USA Spec PA15GM in my '04 Grand Prix for my 4S. It works fine (some opinions on interface programming, but that's besides the point), but without being tied into the OnStar mic answering calls involves unplugging the phone, pulling the phone out of the mount, answering the phone, then placing it on speaker. Is there a Bluetooth headset that I can use and have on while still listening to the phone through the USA Spec unit? Is there a way to tie into the OnStar and use that mic? Just trying to see what my options are.