That'll never happen. An unlocked iPhone would$650-$899. The overwhelming majority of current iPhone users would think long and hard before dropping 3-4 times their initial investment into another iPhone, especially when comparing them to subsidized prices on other phones.
There is no way Apple would cut their own throat by ending carier subsidies.
I think you're forgetting that the "$650-$899" retail cost for the iPhone is mostly artificially inflated and used as a deterrent for anyone considering an "unlocked" phone, almost "forcing" customers to sign up for the two-year carrier contract.
Apple, along with most smartphone manufacturers, are fine with this strategy because they rely on the carriers to promote their phones. In the US, it's not even possible to buy an iPhone from Apple without a carrier contract.
Now compare the iPhone 5s "$650-$899" retail price to the price of Google's Nexus 4 made by LG.
First off, the Nexus 4 has a 4.7" display, 1280x768 resolution and 2GB of RAM, all better specs than the iPhone 5, as well as NFC (near field communication) and wireless charging capabilities, which the iPhone 5 doesn't.
However, the Nexus 4 is retailing for only $299 UNLOCKED and WITHOUT a contract. That's less than HALF the cost of the iPhone 5. However, it's only that price IF you buy it from the Google Play store, which is only avaiable in selected countries.
In the countries where Google Play isn't available, LG is the distributor and setting the price. In Europe, the price for an unlocked Nexus 4 will be EUR 599 or more than TWICE the price of buying it from Google, and bringing it much closer to the unlocked price of the iPhone 5.
Of course you can get it "cheaper" in thoese "LG countries" if you buy it from a carrier and sign the long-term contract.
So that just goes to show you that these "$650-$899" prices for unlocked iPhone and other smartphones are DELIBERATE mark-ups by the manufacturers who are in bed with the carriers to get people to buy from the carriers and sign the contracts.
The manufacturers don't need to charge "$650-$899" for their smartphones to make money on them and in fact, don't really expect to sell many at that price anyway. It's all to just funnel sales to the carriers who then promote these phones over other options. Typical "you scratch my back, I scratch yours" business strategy.
Now if we ever see the government OUTLAW these type of carrier subsidies, then you'll see the prices of these unlocked smartphones tumble down to what they really should be, which is around what the Nexus 4 is selling for.