  Coupled-channel final-state-interaction effects for D and B weak decays into
\pi \pi and K \bar{K} are discussed in a Regge framework. It is found that the
inclusion of coupled-channel effects significantly affects the results obtained
previously in a quasi-elastic approximation. It is also shown that in the
isospin I=0 channel the inelastic final-state transitions (\pi \pi)_{I=0} -->
(K \bar{K})_{I=0} dramatically influence the phase of the B^0 --> (K
\bar{K})_{I=0} amplitude.
