It's on the left hand side of the trunk, behind the carpet lining. It's pretty hard to miss.

Read this tread over at benzworld first. There might be a better way.
http://www.benzworld.org/forums/w210-e-class/1366305-2000-w210-e320-phone-disable-question.html

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'94 E320 with 272,000 miles. '92 500SEL 133,000 miles.
Mods to the '94: TomTom GPS in place of ash tray, Auto Dimming Mirror ,Memory seat, DEI 545T Auto lamps, DEI 530T Auto Up/Down Windows, DEI Remote Start, Motorola Bluetooth® Car Kit, Built in phone charger using factory phone wiring, RainTracker Rain sensing wiper, Keyless Entry, Ambient lighting of center storage compartment. Soon: factory heated seats, REST
Mercedes-Benz is my addiction of choice.
http://www.youtube.com/vanwiek