asterisk users - Jul 2009 - how to remove MWI from a Polycom phone

Hi,

I'd like to disable MWI on certain lines of my IP650 Polycom phone. So I
removed the "mailbox=" parameter from that line's peer section in
sip.conf. Yet the envelope still appears in front of that line and the
phone MWI keeps blinking.

Where should I look to completely disable MWI on a certain line?

Thanks,