Exactly. It'd probably take a while before you actually cost amazon more than what you'd already paid them in shipping plus the cost of all the <78 cent items you sent along with your messages.

While screwing over amazon is noble enough, the end result of people doing this would only result in higher fees for prime and fewer items being eligible for "free" shipping. At the same time, you'd be depriving a very valuable public service of the few cents they ask to offset the cost of message delivery to anywhere in the nation. I'm sure they'd be happy to deliver something besides spam too.