Something

/busy set %query busy
/available set %query available

on *:OPEN:?: {
  if (%query == available) {
    msg $nick AVAILABLE TEXT
  }
  elseif (%query == busy) {
    msg $nick I'm currently busy.  Please type: IMPORTANT, if it's important, and I'll get to you as soon as possible.
  }
}

on *:TEXT:IMPORTANT:?: {
  msg $nick OK, I'M COMING!
}