I bought and fitted this one to my 147 the other day;
http://www.ebay.co.uk/itm/161657760794?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT
It is simple to fit, as you just need to slide the standard stereo out and replace the blank (in my case) CD interchanger connection with the one attached to the connects2 box. I then slid the box into the glovebox and the job was done. It works really well with my iPhone connected via bluetooth, and I can use the steering controls and take calls using the supplied mic. It is great, very pleased indeed. (EDIT: you can also connect an aux cable to the box if you don't have a device with bluetooth, such as my iPod Classic)
It can also be used to plug your phone into and charge via a USB cable, but I have a multi-USB plug in the car that I use for my phone mount.
This is not the only device available to do this, however, and I have heard of others that do the same thing. I cannot remember what they are call, though.