  We point out that the correlation between the large atmospheric neutrino
mixing and the $b \to s$ transition, if exists, comes from the lopsided flavor
structure in SO(10) grand unification theory. We suggest testing the
correlation by studying the deviation of $S_{\phi K_S}$ and $S_{\eta' K_S}$
from the standard model predictions along with the constraints from $\Delta
M_{B_S}$ and $b\to s \gamma$ in a realistic SO(10) model with lopsided flavor
structure. We find a specific correlation between $S_{\phi K_S}$ and $S_{\eta'
K_S}$ that is intrinsic to the lopsided structure and discuss how to confirm or
rule out this flavor pattern by the more accurate measurements of these CP
violation quantities in B decay.
