Loads of them do so, but it's a lottery. Though all will currently give you a message stating "this accessory was not designed for the iPhone...turn to airplane mode yes/no" I simply went around John Lewis plugging it into everything, and using my other phone to call it wile it was docked - some of the early stuff, give really harsh interference.
Just google iphone + <dock name> and it's typical someone has discussed it already.