It's really annoying. I'm sure a later build <KW:> TCU would eliminate it possibly from an X3.

What is does on my iPhone is when you place a call, it reverts to handsfree. Then I will click the audio button on the iPhone and switch it back to handset. Then when the other party answers, it automatically reverts back to handsfree again, and you have to click the button on the phone again, and move it back to handset. After that it sticks.

I sifted through all of the coding options, and messed with a few, but nothing changed it. So, it is most likely a programming issue in the older modules, and since the TCU is not programmable, you have to replace it.