I have now gone from the latest PCCM Porsche Classic Radio back to my Blaupunkt Bamberg. I picked up this device on ebay a few weeks ago, installed prior to my LA to SF round trip and I can say it works fabulously !
Once paired to my iPhone, the device automatically senses a source from your phone. iTunes, XM, or even streaming video. You can control the volume input from your phone as well as from the radio. The source is clear without any ignition interference(common with other bluetooth devices)
Once the source stops, it automatically reverts back to the Bamberg radio (it does not need to be paired again). It will go from stream to a phone call as well. after the call is over, it goes back to whatever was streaming. It will also stream music and give you directions (maps) all at the same time.
I mounted under the glove box with a bit of double sided 3M foam tape. Easy install for the microphone as well.
The sound is really good with these old radio's. The old Blaupunkt is much more analog, and much better than even the lastest from Porsche, more clear and concise sound ini my opinion. This bluetooth converter is all you need to bring your 40+ year old radios (along with some decent speakers) to the modern era.