I purchased my MacBook in January 2007, and it supports A2DP as long as you have 10.5 installed. I imagine 10.5 A2DP works with any built-in bluetooth chipset.

However, the A2DP support itself is really bad. The signal drops out really easily, and the range is way less then using the transmitter that came with the headset. I tried it with both my Logitech Freepulse headset and an iCombi pair. I'm not sure if it's due to the hardware or the driver, so it may be fixed in a later update. I also have a Bluetooth keyboard and mouse, so they may be causing issues.

I would try it in 'doze or linux, but last I checked neither of those had decent A2DP support.

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Andrew