Thanks for the short heads up...I'm about to install the 900BT...so this should help 
Check out my post and look for the "Parking Brake ByPass"One thing to note about the F90BT. You can search high and low and you may not find how to bypass the security setting that doesn't allow you to change destination or watch dvds while driving. In order to do so you must ground the parking break... and then take the black/yellow wire for mute out of the RCA harness coming out of the head unit and put it in the empty spot on the bottom of of wires (empty space between two black wires coming out of RCA leads). This will bypass the F90BT security settings and will work free at all times.
sounds like they got their installation training from best buy. go to someplace elsehey guys the people who install avic near my neighborhood said that if they take out the original stereo unit of the mercedes the car wont turn on. therefore theyd have to rewire the original to the back of the car so that they could install an avic in the front and still have the car turn on. is this true? it sounds so strange no one has said this on the forums