So THAT'S what that thing near the visor is! I was gonna take it out, but wasn't sure if it was part of the phone system.
My car had the complete phone system when I bought it, but after finding out they're too dated to get working again, I pulled it out and tossed it. But still have the antenna, the "black box" in the trunk, and the now-I-know-what-it-is-microphone by the visor. There's also a plug of some kind at the base of the center console at the rear. Must be a phone jack for something, another phone maybe?

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)