Telephone (D-network), block diagram - GF82.70-P-0003-06T

Code (381) MB phone "Standard" in console on right side of dome 1 

Fig 1: Telephone (D-Network) Block Diagram - Standard In Console On Right Side Of Dome

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Code (382) MB phone "CTEL" in console on right side of dome 

Fig 2: Telephone (D-Network) Block Diagram - CTEL In Console On Right Side Of Dome

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.