Apple's begun taking preorders for the new iPhone 6S and 6S Plus, and by all accounts, it looks like another record launch. A lot has happened in the wireless industry since the last time Apple released a new iPhone: All four national cellular carriers -- AT&T, Verizon, T-Mobile and Sprint -- have moved away from the traditional two-year contract, that familiar arrangement that tied you to your carrier but let you buy a basic iPhone at a subsidized price of $199.