Replace Hands-Free System

Hello everyone,
I drive a Passat 3BG and want to replace or supplement the original hands-free system so that my Nokia 6100 can be used with it. There's nothing from Cullmann available as original equipment. THB offers a solution, but it only comes with an external microphone and speaker. However, I'd prefer to use the microphone and speakers already built into the original hands-free system, as the voice quality is better through those speakers.
Here's my question: Has anyone ever modified a phone holder or connected a THB black box to the vehicle's electrical system? Or what other solutions are there? My goal is to connect the THB phone case, with or without the black box, to the original built-in peripherals – the microphone and speakers.

Regards,
Lars.

'So, THB offers an adapter cable that fits the VDA connector and connects to the THB black box. This allows you to use the original microphone and route the output signal to the speakers. It works perfectly for me!!!'

Best regards, Lars.