So here's the news, as first reported by Mark Hearn at SprintFeed and confirmed to Macworld by a Sprint spokesperson: As of November 11, all Sprint iPhone 4S models will be locked to Sprint's own international roaming Micro-SIM by default. However, "Customers in good standing for at least 90 days can request to have their SIM unlocked for international use by calling Customer Care at (888) 211-4727," according to a statement provided by the spokesperson.
It appears that some sort of confusion between Apple and Sprint led to the Sprint models being shipped with unlocked SIM slots at first, despite Sprint's policy to ship worldphones with locked slots and then unlock them only for customers in good standing. The November 11 change is a sign that Sprint's iPhone hardware is now in compliance with Sprint's unlocking policies.
It's unclear about Sprint iPhone 4S models purchased before November 11. They may remain SIM-unlocked forever, though it's possible Sprint will be able to issue some sort of update that locks them.
So, if you're a savvy international traveler who wants the option of using a foreign micro-SIM in your Sprint or Verizon iPhone 4S, now you know the deal: Keep paying your bills, and after 60 days (for Verizon) or 90 days (for Sprint), you can call and request that the carrier unlock your micro-SIM slot. Then you can buy pre-paid cards to your heart's content.
But what about AT&T?
Users of AT&T iPhones aren't so lucky. Because AT&T relies on GSM in the United States, it seems to consider that Micro-SIM slot sacroscant -- it's what ties you to AT&T's network when you're at home -- and as such, will not allow customers to unlock it.
Earlier this year, AT&T had an advantage over Verizon when it came to internationally savvy customers: The CDMA version of the iPhone 4 wasn't a worldphone, so if you wanted to travel abroad most anywhere, you needed to use AT&T. Now the tables have turned: Not only do the Sprint and Verizon versions of the iPhone 4S work overseas, but those carriers' unlocking policies give travelers more flexibility to shop for good deals on international data and voice rates.