  Scaling theory predicts complete localization in $d=2$ in quantum systems
belonging to orthogonal class (i.e. with time-reversal symmetry and
spin-rotation symmetry). The conductance $g$ behaves as $g \sim exp(-L/l)$ with
system size $L$ and localization length $l$ in the strong disorder limit.
However, classical systems can always have metallic states in which Ohm's law
shows a constant $g$ in $d=2$. We study a two-dimensional quantum percolation
model by controlling dephasing effects. The numerical investigation of $g$ aims
at simulating a quantum-to-classical percolation evolution. An unexpected
metallic phase, where $g$ increases with $L$, generates immense interest before
the system becomes completely classical. Furthermore, the analysis of the
scaling plot of $g$ indicates a metal-insulator crossover.
