It'll just be some kind of phone interface, probably a Nokia kit. It'll also probably work still, but you'll have to get a suitable cradle to plug into that socket (oh, and have a compatible Nokia too!).
The headunit looks OE from the photo, so you have to either do a little more investigation or remove it, either way requires the removal of the radio and dash parts.
Bet you've not got as much extra wiring in there as I removed recently from 'the guru' A2 - as he appropriately put it, there were more wires in there than you'd find in an FBI honeytrap!
Cheers,
Mike