AFAIK A2DP is a hardware implementation, and you won't see it on the current iPhone via a software update.
Just because Bluetooth 2.0 supports A2DP doesn't mean Apple implemented it in the iPhone. Remember, the iPhone is *not* Bluetooth-certified, and may not have the full complement of BT 2.0 features in it's hardware.
With that being said, I woldn't hold my breath waiting for A2DP. Heck, I'm just hoping for voice dialing over BT, which IS possible with a software update, but probably won't happen since it'll require too much system space or something.
