Pressing the end call button (the red one) when the phone rings stops the ringer too, fwiw. This is pretty normal behavior for all phones.
(Pressing the End Call button while phone is ringing is the same as tapping Ignore)
http://www.microsoft.com/windowsmobi...yourphone.mspx
That said, it's probably a good idea to mute or vibe your phone before the meeting
From the Today screen, hold vol slider down until the volume drops to 0, then Vibe checkbox is selected, and finally the Off (Mute, whatever
) option selects... so it takes about 3 seconds to mute or vibe the phone beforehand.