  Within a minimal model for the iron-based superconductors in which itinerant
electrons interact with a band of local moments, we derive a a general
conclusion for multi-band superconductivity. In a multi-band superconductor,
due to the Adler theorem, the inter-band scattering dominates the intra-band
scattering at the long wave length limit as long as both interactions are
induced by Goldstone boson (which is magnon in our case) and the transfered
momentum is nonzero. Such kind of interaction leads to a well-known
sigh-reversing superconductivity even if the inter-band and intra-band
interaction are repulsive. This effect can be modeled as arising from an
internal Josephson link between the Fermi surface sheets. Our model is also
consistent with the recently discovered coexistence of superconductivity and
magnetic order in iron-pnictides. Although the experimentally observed isotope
effect is large, $\alpha=0.4$, we show that it is consistent with a
non-phononic mechanism in which it is the isotope effects result in a change in
the lattice constant and as a consequence the zero-point motion of the Fe
atoms.
