This is why these payment plans and buying a phone outright are exactly the same thing, its just a different way to promote it I guess. If you buy a phone at $650, you are still paying for the subsidy in your monthly service fees, even though no subsidy exists. So I am confused as to why people are saying "You're better off just buying at full retail and reselling". This could not be further from the truth. Reselling the phone will get you close to what you paid for it originally, but it won't get you back what you've paid for it in your monthly bills ($20ish?). So either way you go, you're still going to be in the hole.
All aspects of this wireless operator economy come back to cash flow, churn rates, new subscriber acquisition costs, and ARPU (average revenue per user). The comments thus far - unless I missed one that highlighted it - omit any discussion of the impact of churn. The higher the church rate, the more the operator pays to replace customers in order to keep its subscriber count at existing levels. Replacing customers has thus far required phone subsidies up front, i.e. they only pass on a portion of the device price (note: their cost is likely not the same as the MSRP) at the contract signing. Then they gradually recover the subsidy through a portion of the monthly bill, as already noted, but also by avoiding churn. When a customer under the old regime chose to upgrade at, say, 18 months, which is before the contract expires, the operator had to fork over another subsidy of $100-$400. They are partially offsetting this by avoiding churn (and replacement subscriber acquisition cost), but there's no denying that they must be using some portion of the monthly fees to cover the subsidy.
Now, the larger problem the operators are facing is that network expansions are getting quite costly and the level of service must increase. So, as data consumption increases rapidly but monthly and annual ARPU remain relatively flat, the operator must do something to help cut down costs, including the device costs and subscriber acquisition costs. Enter the new phone replacement regime. Now they can leave service pricing where it was (it averaged out costs among all users, right?) and get those pesky early upgraders on whom they burned big $$$ in subsidies to carry a greater share of the financial burden. In the short run, that's what it appears to mean for many consumers. But there is a chance that this new model will enable the operators to offer the consumer a better value in the long run. Instead of seeing increasing service pricing to cover newer, faster, more expensive devices jam-packed with large screens, more memory, etc., consumers will end up purchasing them like they would a regular computing device. Need a fancy model? Great! Don't? No worries! Don't buy one. That's the theory, anyway. Service pricing could be more closely tied to network upgrade, maintenance, and operation costs instead of continuing expansion in the top tier of customers (biggest consumers of wireless data).
It's an expensive business because consumer (including business) expectations are growing so rapidly. Unlike other consumer products which are largely commoditized, at least for 90% of products in their respective markets, e.g. basic DVD/Blu-Ray players for under $100, the mobility segment just keeps expanding as users move into mobile video and video on demand use cases. In 1980 dollars, today's $89 DVD/Blu-Ray player at Walmart would be around $35. The then-current VCR most certainly did not cost only $35. A $500 smartphone in today's dollars would be something like $200 in 1980 dollars. Now, by comparison, the 1983 price on a Motorola DynaTAC 8000X was about $4k. In 1983 dollars. That's over $10k in 2013 dollars! This should give us all some perspective. Even if nominal prices remain stable, the consumer is better off with time since performance improves and inflation keeps on going.
Look for advanced over-the-top services, too, and more machine-to-machine mobile data consumption. Things are really just getting started. The mobile landscape 10 years from now will be amazing to see. I'd really like to see the operators get more control of device pricing so that they could have more flexibility in how they package deals to customers. Yet device manufacturers like Apple don't want to cede pricing control. I guess that time will tell.