Which iPhones support the apt-X codec for Bluetooth audio? I'm shopping for a new Bluetooth headset for my iPhone 4 and noticed that some headsets support the apt-X codec for "CD-quality sound". Presumably this is better quality than plain old A2DP that I've been using so far.

Which iPhones (if any) support apt-X audio over Bluetooth?
No iPhone has native support for apt-X, but you can buy a dongle such as the Sennheiser BTD 300i or a similar one from Creative to enable apt-X support.