Is that the way you think? How easy for The Telco and Apple to dupe you, or, rather, how lazy it is for you to calculate the real cost of owning a new Iphone. Hypothetically speaking, say you had spend USD 200 with a tied in 2 year contract for an Iphone 4 which actually costs only USD 600. Assuming you are going for the USD 75 per month plan from the Telco of your choice, you'd have spend [24 X 75] + 200 = USD 2000 for an Iphone 4. Had you bought your Iphone 4 unlocked, you would spend USD 600 + whatever comparable pay-as-you-go plan which I think probably about USD 40 per month, so your total cost of owning an unlocked Iphone 4 is [24 X 40] + USD 600 = USD 1560.
So, the amount USD 2000 - USD 1560 = USD 440 is the amount of money flying from your pocket to your Telco's hand. And then, you said you would repeat this same cycle again to get the new Iphone? It's like saying you want to sell the Iphone 4 which you bought for USD 600 + USD 440 = USD 1040 for merely USD 300 [a whopping 71 % loss in value in just two short years] to pay for a new Iphone which will again tie you up to a new contract for two money-flying-out-of-your-pocket years. I wouldn't say what you are suggesting people to do as a "smart" move.
In my situation, when the iPhone 4s came out I was able to sell my iPhone 4 on Craigslist for $330 and my wife's galaxy for $100
AT&T let me have a upgrade ( no late payments ) but I had to pay $100 to upgrade my wife to an iPhone 4s ( they could only upgrade one of us)
Bottom line is that if we both had an iPhone 4 I would have come out of pocket a little less because our data plan has not changed.