a ver esto fue lo primero que se me ocurrio, copia pega y prueba
Código:
function makeNumberFormat (value : Object, separator : String)
{
var str : Array = value.toString ().split ("");
var i : Number = 0;
var count : Number = 0
var tmpArray : Array = []
var back : String = ""
str.reverse ();
while (str [i])
{
if ((count % 4) == 0)
{
tmpArray.push (separator)
} else
{
tmpArray.push (str [i])
i ++
}
count ++
}
tmpArray.reverse ();
i = 0;
while (tmpArray [i])
{
back += tmpArray [i];
i ++
}
return back.substr (0, back.length - 1);
}
trace (makeNumberFormat (1000, ","))
trace (makeNumberFormat (10000, ","))
trace (makeNumberFormat (100000, ","))
trace (makeNumberFormat (1000000, ","))
trace (makeNumberFormat (10000000, ","))