You are using one hand and concerntrating on a conversation!you should have both hands free while you drive, some of us still prefer stick gears.
If the phones used hands free and had voice commands they would be ok, but as of today too many doesnt have this thing for their cell phones. Tha makes them too dangerous. In Norway you get fined if the cops see you talk on a cell phone withouth a handsfree set, pretty heavy fine too and it suits them well.