  We prove that two countable locally finite-by-abelian groups G,H endowed with
proper left-invariant metrics are coarsely equivalent if and only if their
asymptotic dimensions coincide and the groups are either both
finitely-generated or both are infinitely generated. On the other hand, we show
that each countable group G that coarsely embeds into a countable abelian group
is locally nilpotent-by-finite. Moreover, the group G is locally
abelian-by-finite if and only if G is undistorted in the sense that G can be
written as the union of countably many finitely generated subgroups G_n such
that each G_n is undistorted in G_{n+1} (which means that the identity
inclusion from G_n to G_{n+1} is a quasi-isometric embedding with respect to
word metrics).
