Having always used Nokia Car Kits the decision to look for units by different manufacturers was a big one. After debating whether to get the Nokia CK-7W, Parrot CK3100 I opted for the HCB-700. What drew me to it was the ability to easily switch between handsets by just pressing a button on the control knob.
Instructions on fitting are clear with only four main wires, these being constant live, earth, radio mute (optional) and live when the ignition is on. All components are clearly marked where to plug into the main "brain". Fitting was straightforward apart from deciding where to fit the LCD and control Knob.
Following the instructions for synchronising phones was straightforward and switching between phones very easy. I can not test the unit to its full potential as I'm using it with a Nokia N70 and Nokia 6230, However; changing the colour of the LCD screen is available and very useful if you want different phones identifed by different colours.
Accepting calls is just a push of a button and if I had a Sony phone voice dial or phonebook dialling would be just as simple.
For those curious about the size of the control knob it sits approximately 4cm high and approx 7cm diameter.
Had this fitted for over a year now, used a variety of different phones with it (Nokia, Motorola, Samsung, Blackberry, Palm, Sony Ericsson) currently using it with an SE850i, phone book syncs no problems, voice dial works with other phones as well, but seems to work better with the SE850i. Not had any issues with any phone I've used with it.