  Black-hole quasinormal modes have been the subject of much recent attention,
with the hope that these oscillation frequencies may shed some light on the
elusive theory of quantum gravity. We study {\it analytically} the asymptotic
quasinormal spectrum of a {\it charged} scalar field in the (charged)
Reissner-Nordstr\"om spacetime. We find an analytic expression for these
black-hole resonances in terms of the black-hole physical parameters: its
Bekenstein-Hawking temperature $T_{BH}$, and its electric potential $\Phi$. We
discuss the applicability of the results in the context of black-hole
quantization. In particular, we show that according to Bohr's correspondence
principle, the asymptotic resonance corresponds to a fundamental area unit
$\Delta A=4\hbar\ln2$.
