Joss - looking at your requirements ( no headset / sound through car speakers etc) I can recommend the Nokia hand free installations. You do need to choose the Nokia handset carefully - I use the Nokia CARK 91 kit with a 6310 which has been excellent - the cradle charges the phone , gives audio through the car speakers with radio mute and you can set up auto answer or voice tags etc.
The 6310 is now a bit old and I'm going to get a EVO cradle convertor to use with a Nokia 6230 which allows me to keep the existing installation but just change the phone cradle.
Of course you could get a handset specific kit now and look at the EVO cradle as an option to change later on.
This won't give you as much flexibilty as bluetooth but gives a very professional installation.
I think that you could also look at the Nokia Wireless Car Kit for extra flexibility.
http://wwwhttp://www.solware.co.uk/m...,21267,00.html
http://www.nokia.co.uk/nokia/0,8764,21267,00.html