Guitar Hero is a rhythm-based game produced by Activision that uses guitar-shaped controllers. The X-Plorer controller was released with Guitar Hero 2 for Xbox 360, and it came with several buttons and ports, including one that looked like a connection for a phone jack. In the Guitar Hero manual, its labelled as an "effects pedal port".
The port in question is unique to the Guitar Hero 2 X-Plorer controllers. When Guitar Hero was first released in 2005, and Guitar Hero 2 was released for PlayStation 2 in 2006, the port was not present on the controllers. It appeared in 2007 with the release of Guitar Hero 2 for Xbox 360. By the time Guitar Hero 3 was released, the jack disappeared from controllers, indicating Activision no longer had any intention of using the port.
The "effects pedal port" was included in the X-Plorer controllers so Activision might, sometime in the future, release an effects pedal. An effects pedal would be an extra device that could mimic real guitar effects similar to the whammy bar the controllers currently have. For example, it might emulate "distortion" or "whah whah" effects used by rock icons. Guitar Hero 2 was released in 2007 and, so far, there has been no sign of an effects pedal release.
The port is an RJ14 jack. This type of a jack is commonly used when connecting a two-line phone. Compared to other "RJ" jacks, the RJ14 uses four wires (or contact points) to host the two lines, as opposed to the one-line, two-wire RJ11, or the three-line, six-wire RJ25. However, although the jack is the same shape as an RJ14, the jack on the X-Plorer controllers only uses two of the potential four wires.
Many video games come with devices which attach via an RJ14 connector. Do not be tempted to attach a device from another game, like a steering wheel, into your guitar hero controller. Because the RJ14 connector in the X-Plorer controller only uses two of the four connection points, other gaming pedals and devices simply won't work. Until Activision decides to release its effects pedal, the connection will remain a useless feature of the guitar hero game.
Do not attempt to create a makeshift device to manipulate the X-Plorer pad's RJ14 jack. Because Activision's proposed effects pedal never made it to production, there is no way of knowing what kind of signal the X-Plorer is expecting to receive. Any such attempts could void any warranty on the controller and permanently damage it.