One theory is that AT&T is paying Apple $325 in cash for every 3G iPhone that will be sold soon. To help ward off phone unlockers and other potential miscreants, the new iPhone will have to be purchased and activated in an AT&T or Apple store, in person. This will probably eliminate almost all of the "buy here, use on another carrier" mentality that many non-AT&T folks would love to accomplish. It also preserves revenue for both companies by tight-fisting consumer control over where they use the device they just purchased.
This kickback that Apple will receive from AT&T for every 3G iPhone sale will make up for all the lost revenue Apple was previously receiving from AT&T on a monthly basis (rumored to be up to $15 per subscriber), according to one analyst. If this is true, then Apple's guidance related to a hit on its profit due to the revenue-sharing arrangement from a monthly stipend to a one-time payment may not materialize as planned.
Sure, millions of new iPhone subscribers pumping in $15 per month into Apple's coffers for at least two years does seem better than a one-time $325 payment from AT&T. Financially, it may be all the same. Over time, it would look better spread out over eight financial quarters rather than in the customer-purchased quarter. Apple gets the money regardless, AT&T gets the subscriber for two years, and the subscriber pays an additional $10 a month over the plan of the older iPhone for the new 3G iPhone. It's not hard to see who wins in this deal.