  The mechanism of spin-phonon coupling (SPC) and possible consequencies for
the properties of high-$T_C$ copper oxides are presented. The results are based
on ab-initio LMTO band calculations and a nearly free-electron (NFE) model of
the band near $E_F$. Many observed properties are compatible with SPC, as for
the relation between doping and $\vec{q}$ for spin excitations and their energy
dependence. The main pseudogap is caused by SPC and waves along [1,0,0], but it
is suggested that secondary waves, generated along [1,1,0], contribute to a
'waterfall' structure. Conditions for optimal $T_C$, and the possiblities for
spin enhancement at the surface are discussed.
