DigiTimes, which gets its info from upstream parts suppliers, says that because cover glass makers are reluctant to invest in the purchase of glass cutting equipment because of the high to the high capital expenditure involved, Apple has purchased 200-300 glass cutting machines to be used by glass makers.
These machines are currently being stored at associated assembly plants; they will be brought online, sources say, once "yield rates for the production of curved glass reaches a satisfactory level."
If it used a curved screen, the iPhone 4S / 5 could be similar in form factor to the Samsung Nexus S, which offered a "Contour Display," as Samsung called it (image above). Just because it used a curved display wouldn't necessarily mean the iPhone 4S / 5 would be in any other way similar to the Nexus S, however.
According to the DigiTimes report, there is no timetable established yet for volume production of the next-generation iPhone. Apple is still sourcing parts, and this information would be in line with recent estimates that next iPhone would launch later than its traditional summer refresh.
Apple itself gave clues in this direction when it said that WWDC would be software-focused, on iOS 5 and Mac OS X 10.7. However, it's rumored that if Apple can get deals with music labels and music publishers in place by then, the company may also introduce iCloud, its cloud-based music service, at WWDC.