I have an extremely good phone: the Siemens Gigaset 4000 comfort. This phone has a handsfree function that is no less than excellent. With most phones I've used before this one, the person on the other side could always hear it that I was calling handsfree. With this phone they cannot.
It's so good even that I ALWAYS phone handsfree nowadays. Holding a phone to my head actually starts feeling strange. The mic in this phone is good enough to be able to put the phone up to 2-3 meters away, and talk normally without the person on the other side noticing it. It's truely the best phone I've ever owned, and I can't recommend it enough!!