  The theory of $CP$ violation based on phases in weak couplings in the
Cabibbo-Kobayashi-Maskawa (CKM) matrix requires the phase $\gamma \equiv {\rm
Arg~} V^*_{ub}$ (in a standard convention) to be nonzero. A measurement of
$\gamma$ is proposed based on charged $B$ meson decay rates to $\pi^+ K^0$,
$\pi^0 K^+$, $\pi^+ \pi^0$, and the charge-conjugate states. The corresponding
branching ratios are expected to be of the order of $10^{-5}$. (submitted to
Physical Review Letters)
