  We evaluate the tree level four fermion string amplitudes in the TeV string
mass scale models with intersecting $D6$-branes. The coefficient functions of
contact interactions subsuming the contributions of string Regge resonance and
winding mode excitations are obtained by subtracting out the contributions from
the string massless and massive momentum modes. Numerical applications are
developed for the Standard Model like solution of Cremades, Ibanez, and
Marchesano for a toroidal orientifold with four intersecting $D6$-brane stacks.
The chirality conserving contact interactions of the quarks and leptons are
considered in applications to high energy collider and flavor changing neutral
current phenomenology. The two main free parameters consist of the string and
compactification mass scales, $ m_s$ and $ M_c$. Useful constraints on these
parameters are derived from predictions for the Bhabha scattering differential
cross section and for the observables associated to the mass shifts of the
neutral meson systems $ K-\bar K, B-\bar B, D-\bar D$ and the lepton number
violating three-body leptonic decays of the charged leptons $\mu $ and $ \tau
$.
