Griffin SmartShare Headphone Splitter + Adapter for iPhone

Overview
Griffin's Headphone Adapter lets you use your favorite headphones in the compact headphone jack standard on iPhone. Even better, when you add SmartShare you can plug two sets of headphones into one headphone jack--so you and a friend can listen and set your own volume level.
Features
Adapts headphone or earphone plugs to the compact jack on your Apple iPhone
Lets you and a friend listen together; you can both control your own volume level
This accessory is compatible with the following:
iPhone