I have an iPhone 4S, the original iPhone 4S AC to USB adapter, and a generic Dynex brand 30 pin cable. When ever this cable is connected to the iPhone sound will not play over the built in iPhone speakers. If headphones are plugged in they work fine, but when they are removed sound will not play on the iPhone's built in speaker. If I swap in the original cable that came with the iPhone it works as expected. Any ideas why the iPhone 4S thinks this cable and configuration is a line out source?