Prepaid vs. Contract

Within the past two months I have come to realize that with more and more prepaid companies coming around with unlimited this and unlimited that, sales for them have gone up increasingly. With Boost Mobile, Metro PCS, Cricket, and so on making things cheaper and cheaper it rises the question how if at all is this affecting the carriers? What if anything are they doing to compete? Or what makes them different then all the rest of the companies? I will have an interview with at least one AT@T rep and hopefully a Verizon rep to answer these questions for me us. So stay tuned.