[lotharbot]

The decision cites federal law: "to possess the images in the cache, the defendant must, at a minimum, know that the unlawful images are stored on a disk or other tangible material in his possession".

Text and pic messages are push, but (at least on my phone) pictures aren't downloaded until you access the message, at which point it's marked as "read". So at least one valid defense is to have not accessed the message -- you can't knowingly possess it in that case.

What if you've already accessed it? US CP laws explicitly allow an "affirmative defense" [0] if you possess only a small number of images and, upon discovering this possession, either immediately destroy them or immediately turn them over to law enforcement [1]. So if you receive a sext message from someone underage, quickly deleting it should shield you from prosecution (IANAL TINLA [2].)

[0] http://en.wikipedia.org/wiki/Affirmative_defense - in essence, affirming the facts of the case, but offering a justification/excuse that demonstrates one is not culpable.

[1] http://www.law.cornell.edu/uscode/text/18/2252A section (d)

[2] http://en.wikipedia.org/wiki/IANAL