Bluetooth Headset Profile and the Nexus 7? I purchased the Nexus 7 3G to install as the radio in my vehicle. I stream all media from the tablet via Bluetooth to my factory head unit.
However, I have two main issues to solve before this becomes a feasible replacement:
1) I cannot set the microphone on the Bluetooth unit to work with the tablet.
The tablet ends up using the built-in mic; and since that is located behind the dash, it doesn't work so well. I have been researching on Google and XDA for months trying to find a solution. From what I have read, this is my current assumption: Tablets in the USA are not built with phone functionality on purpose to deter people from buying a tablet and using it as their primary phone.
It seems no big deal just learn how to hack to enable phone functions and that would activate the proper Bluetooth headset profiles to work with the external mic on a Bluetooth unit. So after a ton of research I have successfully unlocked, rooted and installed TWRP as well as edited the bool.xml in framework-res.apk to make the Nexus 7 voice capable. But still I have no external Bluetooth mic support.
Is this a problem with Android in general? or Jelly Bean in general? or all tablets?
At this point I have exhausted all that I can do on my own without asking for help. Does anyone know how to use an external Bluetooth mic on the Nexus 7 3g 4.2.1?
2) My second problem is the tablet will not consistently reconnect with the Bluetooth head unit every time the vehicle starts.
Sometimes it connects properly with phone and media profiles; sometimes just one of the two, and sometimes none at all. I have used the Tasker app as well as the Bluetooth auto connect plugin, but it still is very flaky at best.
I have never owned an Android device before this tablet, always Apple stuff that to be honest just worked right out of the box. But I love the customization available on Android especially for an in-car install. So again is this an Android issue, Nexus issue, or a tablet issue? It seems from the research I have done that most Android phones will auto-connect but these tablets seem to be missing certain Bluetooth settings or profiles that cause them not to work. So any ideas on how to solve this issue?

At this point, if I can not resolve these two issues, I am going to return the Nexus 7 3G and get a Samsung galaxy tab 2 7.0 3G P3100. From what I can tell, this tablet is a fully functioning phone right out of the box, so hopefully would solve my two issues above. But since this Nexus has MUCH better specs and is cheaper, I am hoping to find an answer to my Bluetooth problems.
Its not only your device's issue, but also in most of the devices. Android 4.2 has this issue. And Google officially confirmed it . 

Look above link
"We have fixed the a2dp streaming stutter problem on N7. The next release should have the fix.Sorry about the problem." 

Android 4.2.2  fixed Bluetooth audio problems on Nexus phones and tablets. You just try it out by using new 4.2.2 in your N7.