Not that I would advocate such activity, but unless there
exists an extradition treaty that allows for computer trespass
or denial of service attacks, I imagine that a few weeks of
being hacked and DoS attacks would have them reconsidering
the fee's that they charge to spam houses. Or they could
be put on the RBL list, and i imagine people that are using
.to for non spam reasons, would demand something be done.
Despite other's protest, there is accountablility in the Internet
even without accountability in local, state, federal, or international
courts.
There seems very little risk involved in doing something active
to solve the problem due to the nature of international law, etc.
(If they sue you in a Tonga court, what good will that do? If the
sue in a us court what basis can they claim if they are really
part of Tonga, at any rate in action in the US opens them up to
legal action from you.)