Apple iPhone TTY Adapter
Contrary to popular belief. Apple's iPhone TTY Adapter ($19) is not a 3.5mm headphone plug-to-iPod adapter -- it's an adapter that enables an iPhone to be connected to a TTY text telephone terminal, primarily used by people with hearing or speech issues. When connected to a TTY device through the small port, iPhone can relay typed messages to another TTY device or a relay service, where a human will read the messages to a recipient who can hear them. Note that the photo shows how 3.5mm headphone plugs are too big for the hole.