I, too, dislike the start-up and shut-down 'music'. I've gotten into the habit of pressing the # key immediately before turning the phone off, and then again immediately after turning the phone on.

Selecting the Meeting option or pressing the # key will silence the startup sound but they will ALSO silence all ring tones...... so you want to hear your phone ring when someone calls you can't use either of these features.

I found that if I went to Settings, then Sound, I could choose "Meeting" instead of "General.

you can hold down the # key to switch to vibrate mode so you can at least turn the phone on and off fairly easily without that terrible noise

There is no info about in the manual. I think it's not possible.