[SmellyGeekBoy]

I always saw the "Sent from my iPhone" footer as nothing more than advertising, and the ensuing "Sent from my x" as a small act of rebellion or tongue-in-cheek reference.

I hadn't considered that it was intended to act as a warning that the content might be more error-prone.

[taeric]

I've seen a few that were direct statements of more typos because of the device used. Probably did start and largely remain advertising, though.