I have a Nokia hands free kit and have a combined power antenna on the left rear quarter. The OEM radio antenna is exchanged for a power antenna for both radio and cell phone (Hirschmann). My microphone is mounted near the rear view mirror (original MB europe mount) and I have my cell phone cradle mounted on an original MB console with speaker.
I have build in a lot of hands free kits in the past and have mounted the microphones on the left A pillar, near the left sun visor or near the rear view mirror (depending on type of car and main usage). I have most of the speakers either under one of the dash panels (just above ventilation holes), behind the ashtray lid (in non-smoking cars) or under the passenger seat (if the speaker was not too high).
greetingz,