Apple says that most iPod accessories that use the 30-pin connector â?? such as chargers and speakers â?? may also be compatible with iPhone, even though they haven't been certified as "Works with iPhone."
The company also notes that connecting uncertified accessories will result in a prompt to enter Airplane mode, which should obviate potential interference issues:
"When you connect an uncertified accessory, your iPhone will notify you and present you with the option to go into Airplane Mode, which turns off the communication capability of the iPhone while it's connected to that accessory. This means that youâ??ll avoid potential audio interference, but you'll be unable to make or receive calls. If you choose not to enter Airplane Mode, you can make and receive calls, but you may experience some audio interference."