So I have a JVC KD-R821BT car stereo for about a year or so. Things worked flawlessly with my old iPhone 4s which was on 5.x. Now that I have an iPhone 5 on 6.xx, I'm still able to pair and unpair, hear music via Bluetooth without any dropouts. I can access my phone book and I can still make and receive phone calls via my car stereo. All of this without having to jailbreak/safe mode/whatever.
But here's my thing - although I said I can make and receive phone calls via the JVC/Bluetooth/iP5, this function is next to useless since I got my iP5/iOS 6.xx because the called/calling party reports it can't understand me at all. They report my voice is utterly distorted.
At first, I was angry about Apple as most of us here are. Then I checked with JVC and found out that since February, they are offering a firmware update for a lot of their models which has "correcting Bluetooth issues" as a single release note. Of course, for my car stereo, there is no update available! So I contacted JVC customer support asking for help. I said that they are obviously aware of that problem due to the fact that there actually are firmware upgrades available for a lot of other models. Brief reply: "At present, there are no firmware upgrades available for your specific model. Statements about further developments are not possible. We regret to not being able to give you any other answer than this."!
Since I received this answer, I'm not angry with Apple anymore. I realized that Apple obviously upgraded (or at least changed) BT support within iOS to the latest version or something like that and that JVC actually are the ones NOT following that BT development, at least not on my specific car stereo model, even though they could which is proven by making firmware upgrades available for other models. Most likely, this is where my problems arise from. I don't know anything about backwards compatibility between Bluetooth versions, but it seems obvious that there is no backwards compatibility here.
The thing bugs me most is that it wouldn't help to get a new car stereo. Who knows - the BT support within iOS may change again in a couple of weeks or months, and if there weren't any firmware upgrades for a possible new car stereo (like at present with my old one), I'd be fooled again. And as I'm not willing to spend a couple of hundreds of bucks every few months for a new car stereo, I will leave the situation as it is at the moment. I still hope that there might be a firmware update for my current JVC car stereo someday.
Happy Easter everyone.