This PC World article was reprinted in the NYT: Put an end to cell-phone spam., by which they mean text message (SMS) spam.
It's solid. Links to AT&T services that can eliminate email to SMS, abilities to change your SMS identifiers, using spam filtering services, etc.
SMS is a real hack, a billion dollar industry built atop a phone service never intended for human use. Interesting business lesson there.
As a hack it has no defenses at all, and incoming spam costs money.
I think that's why the iPhone team isn't keen to support MMS or SMS -- it's aesthetically revolting and an endless font of costly spam.
So, good advice, but the real solution is to dump SMS.