The 16GB version of Sprint's iPhone 4S had already completely sold out for pre-orders, but the 32GB model and the 8GB iPhone 4 are now in "limited quantities," which presumably means they'll sell out before too long. Interestingly, Sprint isn't accepting any backorders — perhaps a sign that they're not sure how or when Apple will replenish stock — so if you had your heart set on a 16GB Sprint model, you're out of luck in the short term.