Dock speakers connect to the iphone through the same interface. The high end ones have ARM cores, they have wifi, they might even run Linux. There is a theoretical chain of trojan --internet--> PC --wifi--> speaker --usb--> iphone.

This is, of course, insanely unlikely today. But in a few years, when everything has a 1GHz ARM core and an internet connection, we very well might start seeing malware that jumps devices and infects entire households.