So the goal was to replace this

With This

First thing was to strip off he BT handset.

Quite easy. At the end you stay with a little pcb board connected to a mic, two speakers (ear and bell) and the USB socket and battery.
In the process the speaker for the ringtone was disconnected, so i cut it out.

The Beocom was also dismantled, just keeping the front part+keyboard and the hull.

The things did get quite well:

- The POP BT Mic did fit perfectly in the little ribber that keep the become mic in place.
- I removed the BT POP speaker and use the original Beocom one thus preventing the use of any glue or something to fix it.
- I plan to also use the ringtone speaker but didn't try it yet.
- The main BT POP PCB can be installed inside in a way that the main button (hang in, hang off)  stay in front of the center wheel button.
The other buttons (Volume +/-) are lost.
- USB socket is two wire, so they must be a way to connect it to the original charging pins of the Beocom (to do). 
- Appart from the central wheel button, anything else is non-working. The BT POP status LED can be seen through the LCD screen. 
- Two screw holes are conveniently placed to secure the BT PCB with a little plastic strap. I use a o'ring to adjust the PCB height in order to not have the button continually depressed. that was the most difficult part.
- The hull will need a little cutting to give room for the PCB. Nothing difficult as the plastic is quite soft.

Here is what it look before closing it.

Now, the "replace that by that" shot was made this morning, that is with the work done !

So it works ! Now i need to connect the ring speaker and manage the handset to charge when on the base.

For people who are alarmed by this, i would like to say that the working handset and the base are untouched (just disconnected the wire).

I just screw up a non working beocom PCB and a hull (internally).

(Guy, special dedicace, hope you'll find this post !)

Yes - following with interest - looks great so far!

Is the silver piece (up near the speaker) the battery?

Hey, Happy, you see it !

Yes it is the battery. it's secure by it's original double side tape.

Are you going to modify the charger to produce 5V (usual USB output) or accept the 5.6V that it usually produces?  Perhaps add a series diode inside the handset?