What type of data jack is between the headphone and power jacks?

There are three jacks on the right side of the Nokia 2600c-2b: on top, there is a headphones jack. On bottom, there is a power jack. In the middle, there is a jack that looks like data port, but is not a standard USB jack. What is the official name for this jack type? I need a cable to connect from my computer to this jack in order to revert the phone's "Cannot Undo Restriction" state -- see http://www.unlocks.co.uk/cannot-undo-res....

Thanks!