Handsfree Mobile in MB Actros-2 truck

This truck comes standard with buttons (answer/hangup) on the steering wheel for handsfree mobile phone use. However, other than the built-in buttons, the reset is an extra cost option. To use handsfree mobile, I know there is a fancy handsfree accessory kit available from Mercedes-Benz, but that is very expensive.
I have heard that it can all be done much more economically. All that is required is a cheap Nokia mobile phone (probably other manufacturers also work) that you hide in the console/overhead, and an adapter cable to connect the mobile phone. Are there instructions anywhere for making this adapter cable and installing it? Perhaps, this adapter cable is available for purchase somewhere?



