I recall there was some understanding that it had a legitimate use as well as the obvious marketing, which was to advise the reader that the message may be unex

I recall there was some understanding that it had a legitimate use as well as the obvious marketing, which was to advise the reader that the message may be unexpectedly concise or contain errors because it was sent from a cell phone, something less common before the iPhone came out. BlackBerry phones did this too for the same reasons.