  We consider quantum mechanics on the noncommutative plane in the presence of
magnetic field $B$. We show, that the model has two essentially different
phases separated by the point $B\theta=c\hbar^2/e$, where $\theta$ is a
parameter of noncommutativity. In this point the system reduces to
exactly-solvable one-dimensional system. When $\kappa=1-eB\theta/c\hbar^2<0$
there is a finite number of states corresponding to the given value of the
angular momentum. In another phase, i.e. when $\kappa>0$ the number of states
is infinite. The perturbative spectrum near the critical point $\kappa=0$ is
computed.
