  We present a study of the basic microscopic model of an $s$-wave
superconductor with frustrated interband interaction. When frustration is
strong, such an interaction gives raise to a $s+is$ state. This is a $s$-wave
superconductor that spontaneously breaks time reversal symmetry. We show that,
in addition to the known $s+is$ state, there is additional phase, where the
system's bulk is a conventional $s$-wave state, but superconducting surface
states break time reversal symmetry. Furthermore, we show that $s+is$
superconductors can have spontaneous boundary currents and spontaneous magnetic
fields. These arise at lower-dimensional boundaries, namely, the corners, in
two-dimensional samples. This demonstrates that boundary currents effects in
superconductors can arise in states which are not topological and not chiral
according to the modern classification.
