  We point out that in (open) string compactifications with non-zero NS-NS
B-field we can have large Kaluza-Klein thresholds even in the small volume
limit. In this limit the corresponding gauge theory description is in terms of
a compactification on a non-commutative space (e.g., a torus or an orbifold
thereof). Based on this observation we discuss a brane world scenario of
non-commutative unification via Kaluza-Klein thresholds. In this scenario, the
unification scale can be lowered down to the TeV-range, yet the corresponding
compactification radii are smaller than the string length. We discuss a
potential application of this scenario in the context of obtaining mixing
between different chiral generations which is not exponentially suppressed - as
we point out, such mixing is expected to be exponentially suppressed in certain
setups with large volume compactifications. We also point out that T-duality is
broken by certain non-perturbative twisted open string sectors which are
supposed to give rise to chiral generations, so that in the case of a small
volume compactification with a rational B-field we cannot T-dualize to a large
volume description. In this sense, the corresponding field theoretic picture of
unification via Kaluza-Klein thresholds in this setup is best described in the
non-commutative language.
