Cheiron if you go the route of using an on input maybe have away to turn it off n on maybe something like this..

#modem off
on *:input:#:if ($regex($1,/^([+-]m)$/S)) .timermode 1 1 mode # $regml(1) 
#modem end
menu channel {
  -
  .Turn $iif($group(#modem) = on,Off,On) +/- m:{
    $+(.,$iif($group(#modem) = on,dis,en),able) #modem
    echo -a +/- m is now $group(#modem)
  }
  -
}