for the three types of spectra [@PPSNO2bb]: ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \gtap 2.8\times 10^{-2}~{\rm  eV}$ (IH), ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \gtap 0.06~{\rm  eV}$ (QD) and ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \ltap 2.0\times 10^{-3}~{\rm eV}$ (NH). At 90% C.L. the indicated lower and upper bounds read, respectively: ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \gtap 1.5\times 10^{-2}~{\rm  eV}$ (IH), ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \gtap 0.25~{\rm  eV}$ (QD) and ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \ltap 6.0\times 10^{-3}~{\rm eV}$ (NH). The quoted lower bounds are in the range of the sensitivity of currently operating and planned -decay experiments (see further). These results imply, in particular, that a measured value of ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! \neq 0$ (or an experimental upper limit on $\!\!$) of the order of ${\rm few} \times 10^{-2}$ eV can provide unique constraints on, or even can allow one to determine, the type of the neutrino mass spectrum in the case the massive neutrinos are Majorana particles; it can provide also a significant upper limit on the mass of the 