why does the iPhone have huge interference?

The 850 MHz frequency of AT&T’s GSM network and the iPhone’s radio is low enough on the radio frequency spectrum to cause a type of Frequency Modulated (FM) distortion which is picked up quite readily by all unshielded electronic components. Most consumer electronics do not have this shielding in place (your 20–25 foot long speaker wires can and do function like antennas in such cases), but eventually any part of your component system that is not shielded can “pick up” this signal and your system will amplify it.

Rectifying this problem can be costly and in some cases be impossible without a complete replacement of your a/v system, but in the case of small / portable systems, shielding may be as simple as re-cabling or replacing your speakers with magnetically shielded speaker enclosures.

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