One of the reasons that Apple is doing so well financially is that the iPhone 4S, which was released last October, still has a lot of momentum. And now five additional regional carriers in the U.S. will start offering the iPhone on April 20. Oddly, they'll be selling both the iPhone 4S and iPhone 4 for $50 less than the other carriers, starting at $150 and $50, respectively. In addition, the GSM carrier in the bunch will also likely offer the iPhone 3GS.