Up until now, Sprint's iPhone 4S was being sold to customers with the SIM card unlocked, meaning you could theoretically slide a non-Sprint SIM in there while overseas and avoid the carrier's standard roaming fees — but that's not happening anymore (at least, not without jumping through some customer service hoops). A new document obtained by SprintFeed suggests that starting today, the phones are being sold SIM-locked as you'd normally expect. Interestingly, customers who've already picked up and activated their 4S won't be impacted; in other words, their SIMs remain unlocked.