Lack of audio or cell phone functionality may be related to the failure of the audio gateway module.
Car Problem Reports
Mercedes-Benz E320 BLUETEC Failed Gateway Module May Cause Lack of Audio/Cell Phone Functionality
Mercedes-Benz E320 BLUETEC Problem
Visitor, 2009 Mercedes-Benz E320 BLUETEC, 10,000 mi
The connection via bluetooth is sub-standard and Mercedes dealer admits 200d command module is weak. No problems prior model years and dongles or with 2010 and after. Seems rediculous that MB will not address this beyond saying that was a bad year for our bluetooth. impossible to use phone reliably hands free.