My 3G iPhone works great, but causes an inductive buzz on pretty much anything with speakers within a 5′ radius. After some googling about, I came on the approach of using an anti-static bag (sometimes called ESD packaging). If the phone is shielded by the bag it knocks down the buzzing almost completely, while still allowing the phone to stay in touch with the tower.
With some experimenting, I have found a small tray with curved sides – just setting the iPhone in the tray on top of the bag solves the problem.
There’s a product idea in here somewhere. In the meantime you can order ESD bags and trays from here: http://www.correctproducts.com