I recently bought a used 2005 SL500 and there's no MHI Hands Free Cradle in the arm rest, is there any other place it could be, I checked and can't seem to find it?
It is typicaly in the glove box. That's where MB installs them.
I guess I would check the glove box as well.
You may not have it. Get the datacard for that car from online Mercedes vin decoders or from the dealer and it will tell you if you have it installed.