FWIW, on my Moto Droid X, if I have the phone in vibrate mode, then it will shut down and start up silently. (It will buzz, though.) This seems to be the only way to defeat the otherwise-piercing scream it makes, mid-boot, when it discovers the SD card. "Oh, an SD card! Hurrah!"

Also FWIW, our 2005 Acura TL is dead silent about its Bluetooth handling. There's a discrete icon on the dash to tell you it has a paired phone. For contrast, our 2008 Audi A3 has no discrete icon. Instead, it will interrupt the stereo for two seconds to play a loud chime when paired and another loud chime when unpaired. If there's a way to defeat this, I haven't found it yet.

(And neither car supports A2DP audio. I was recently in a series of rental cars and was deeply impressed by Hyundai. Pairing was easy. A2DP audio just magically worked. I was less impressed with Ford Sync. Pairing required me to type a 6 digit PIN into the phone (*). Then, every time the car started, it somehow started up my DoubleTwist music player, even though I really would rather have been using Pandora. I'm not sure whether to blame this one on my phone or on the car for saying "hey phone, start playing.")

(*) Security wonkery: I understand that the PIN is a feature to keep an interloper from pairing with your car. However, the simple Hyundai system relies on the fact that it's only actively willing to pair with a new phone when you select the menu item in the car. So far as I can tell, you can't just walk down the street and pair with a random Hyundai that's driving by.