IMHO, in light of the possible prior art, it may be very probably that
the potential patent application is invalid or will not approved.
Therefore, it might be feasible to ignore the IPR claim all together
and
preceed with approval of Sender-ID.
Oh dear.
Never, *ever* make the mistake of thinking that a patent application
will not be approved because of prior art.
You'd be stunned at the things which are granted patents where the
prior art seems *so* obvious to anyone who knows (and that is a key -
the guys at the USPTO can't know everything, and it is not their job to
know everything).
Right now the MO at the USPTO seems to be "approve everything, and let
them sort it out in the courts".
Anne