One of the advantages to the newer generation of smartphones is excellent dock integration. Depending on the device, you can have desktop mode or car mode. On some Motorola devices, you can can do a little bit more than that. However, docks that provide all the functionality are typically more expensive than docks than can do just one thing. Now, there is a hardware mod for AT&T HTC One X docks that will let them do both at the flip of a switch.
XDA Forum Member ModemJunki released a hardware tutorial that turns a cheap dock into a dock that can be used for both desktop and car modes. ModemJunki explains how the modes are triggered:
The signal to go into dock mode is triggered with a resistor between pins 4 and 5.
10kOhm triggers auto dock mode
68kOhm triggers desk dock mode (also, a 47kOhm triggers desk dock mode)
In the tutorial, users will need a cheap dock they can sacrifice to a good cause. They will then take it apart and make the proper modifications. Among the mods, is a switch that users can flip to trigger desktop and car modes. Once completed, users simply have to put the One X in the dock and flip the switch depending on which mode they want.
For the full tutorial with instructions, pictures, and video, check out the original thread._________