  We discuss implications of recent experimental data for B decays into two
pseudoscalar mesons, with emphasis on those with $\eta$ and $\eta'$ in the
final states. Applying a U-spin argument, we show that tree and penguin
amplitudes, both in $B^+ \to \pi^+ \eta$ and in $B^+ \to \pi^+ \eta'$, are of
comparable magnitudes. Nontrivial relative weak and strong phases between the
tree-level amplitudes and penguin-loop amplitudes in the $B^{\pm} \to \pi^{\pm}
\eta$ modes are extracted. We predict possible values for the averaged
branching ratio and CP asymmetry of the $B^{\pm} \to \pi^{\pm} \eta'$ modes. We
test the assumption of a singlet-penguin amplitude with the same weak and
strong phases as the QCD penguin in explaining the large branching ratios of
$\eta' K$ modes, and show that it is consistent with current branching ratio
and CP asymmetry data of the $B^+ \to (\pi^0, \eta, \eta') K^+$ modes. We also
show that the strong phases of the singlet-penguin and tree-level amplitudes
can be extracted with further input of electroweak penguin contributions and a
sufficiently well-known branching ratio of the $\eta K^+$ mode. Using SU(3)
flavor symmetry, we also estimate required data samples to detect modes that
have not yet been seen.
