Well, having already removed my head unit to install the PIE Ipod adapter, I removed it again to install a Parrot CK3100 LCD Bluetooth Hands Free Kit.
I bought it here and used the Toyota harness which makes installation a snap:
The install was very straightforward and the harness is goof proof, since the connections only fit together if they are done correctly. I ran the microphone to the pillar adjacent to the driver side door, and mounted the LCD display unit using the vent adapter included with the CK3100 kit (there were several different adapters for mounting both the microphone and the LCD unit) on the air vent to the left of the center display.
Well, let me tell you this thing rocks! When a call comes in, all speakers are muted and the LCD displays the number (and name if it is in your cell phonebook). The unit automatically syncs with your cell once you start the car, and the LCD reads out battery life on the cell, and the signal strength of the cell. There are voice commands to make calls, and keywords to use the phone (eg "Telephone" to make a call, etc.).
I found this post prior to ordering my unit right here on TN that was helpful:
Anyone that did not get the factory bluetooth and has a need for hands free should give this kit a look see. Only $200 and an easy do it yourself.