I set up my boss with a Parrot CK3000.
    http://www.expansys.com/product.asp?code=PAR_CK3000
He had it installed by a local shop and it worked great for a week
or two.  Then it went to pot.

We went a few rounds with the service guy and even swapped out the
unit.  It didn't improve.  It was very frustrating.

Bottom line - they *can* work well, but I recommend buying from the
shop who does the installation.  I don't know of any such shops,
but not doing so is asking for a bunch of finger pointing if things
go wrong.

--kyler