  We study the compactification of OM-theory on tori and show a simple
heuristic derivation of the $S$-duals of noncommutative open string theory in
diverse dimensions from the OM-theoretical point of view. In particular, we
identify the $S$-duality between noncommutative open string theory and
noncommutative Yang-Mills theory in $(3+1)$ dimensions as the exchange of two
circles of a torus on which OM-theory is compactified. Also, we briefly discuss
$T$-duality between noncommutative open string theories.
