Some general thoughts. I purchased an '07 Solara NAV (from OEMValue) unit to put on our '05 4Runner with JBL. The install was easy. I added on Terk XM also. However it did not have the NAV voice capability (that is speaking to you). There were threads on how you had to run a wire from the NAV to the Amp so I tried it twice but was never successful to get voice working. Therefore the mic was a moot point as was bluetooth. Lost a bit of functionality. I still have the original HU and put it back in whenever I need to.
I don't know how it interfaces with the Camry though.
I have just removed our TCH NAV to hook up a SoundLinq XM interface. Removal and reinstallation is something anyone can do unless they are really timid.
Here is a link on how to get the NAV unit in/out.