This sounds like a 10 page side story in a Neil Stephenson Book. I love it.
The author is also a relatively prolific HN poster (https://news.ycombinator.com/user?id=cstross).
The spam tries to act like a perfectly normal message as long as it is talking to the spam filter, and as soon as it thinks it is talking to a real person, it shows its spam message. The spam filter tries to impersonate the recipient as best as it can (in 3D video), meanwhile trying to figure out whether the message is spam.
The spam filters are unfortunately humstrung by the fact that they can only become close to real conscious AI and not further, because taking them all the way there would mean you'd be exposing a conscious being to spam all its life, which would be torture and thus criminal. Spammers don't care.
IIRC, this is just a side anecdote in some paragraphs somewhere, but I love it.
I don't know anybody like Egan, he takes the science part to such extremes... My favourite SF author is Iain M Banks, but you're probably already familiar with him.
Whether Comcast would want to make it that easy for people to cancel is entirely a different issue though :)