Samsung SGH-A637CWAATT - Manual (Page 35)

Call Functions 32
In Silent mode, your phone’s speakers are muted. An incoming
call causes the phone to vibrate and light up, depending on the
settings of the Silent Phone Settings feature.
To exit and reactivate the previous sound settings, press and hold
again until “Normal Profile on” displays. The Silent mode
and Vibrate icons are no longer displayed.