To expand upon your code..
Code:
on *:text:!list?:#yourchannel:{
  var %file = lists\list.txt
  if ($+(%,rules.timer,$nick)) { return }
  if ($ini(%file, $2)) {
    .play -nm1t $+ $2 $nick %file
    set -u10 %rules.timer $+ $nick On
  }
}

Although this example won't take the format '!listA', but '!list A'..