  NMR, EPR and magnetization measurements in Na$_x$CoO$_2$ for $0.65\leq x\leq
0.75$ are presented. While the EPR signal arises from Co$^{4+}$ magnetic
moments ordering at $T_c\simeq 26$ K, $^{59}$Co NMR signal originates from
cobalt nuclei in metallic regions with no long range magnetic order and
characterized by a generalized susceptibility typical of strongly correlated
metallic systems. This phase separation in metallic and magnetic insulating
regions is argued to occur below $T^*(x)$ ($220 - 270$ K). Above $T^*$ an
anomalous decrease in the intensity of the EPR signal is observed and
associated with the delocalization of the electrons which for $T<T^*$ were
localized on Co$^{4+}$ $d_{z^2}$ orbitals. It is pointed out that the in-plane
antiferromagnetic coupling $J\ll T^*$ cannot be the driving force for the phase
separation.
