I put one in mine this morning, however this was to replace a metavoice system so the wiring was already there. I wired it up as if bose was fitted because I intend to fit an amplifier at a later date so wiring it into the green mini iso socket for the parrot output and mute was important. That way the head unit cuts the sound rather than the parrot disconnecting the speakers.
Things to watch out for:
Theres no ignition switched feed to the head unit so you can take a feed from either: the switched lives in the switch (fog lights/hazards/boot release/central locking) multisocket below the radio or the cigarette lighter socket.
You can either tap into the wires already in the back of the green mini iso socket or buy a y connector from ebay/bluespot they're about a tenner.
You may have a handsfree connection already installed in your car! It's a clear/opaque six/eight pin connector that is the first branch off the main wiring harness that goes to the back of the radio, working back into the car, if that makes any sense. If you have, go to somewhere like Nexxus and buy the parrot loom for your car and it is really just plug and play. Not all 147/156/GT's have them - all 3 of my 147's did, my 159 did, but my GT blackline didn't - and that's the most recent! - do a search on this site - there's some really good information and pictures to help. The head Unit's got the wiring connections on a label on the back of it too.
146 1.6TS, 156 2.0TS, 156 1.8TS, 147 1.6TS, 147 2.0TS, 159 1.9JTS, 147 1.6TS, 159 1.9JTDm, Mito 1.4, GT, Giulietta 2.0JTDm, Giulietta 1.4tb, Giulietta 1.6JTDm........