I have an echo in my BMW as well, it was not there with the 2G iPhone. Here is what will happen... Apple will blame BMW, BMW will blame Apple and we will have to live with a slight echo until they can put their egos aside and find a fix to it.
Edit: Also if you have the factory installed BMW iPod integration you cannot charge your iPhone 3G from the dock connector, my 2G charges fine on it as well as my iPod Classic. You can play music just fine but the display says "This accessory does not support charging". This is another issue with BMW integration. I personally think its Apple's issue, but let the blame game begin.