Steve Jobs' team are said to have purchased between 200 and 300 glass-cutting machines, specifically in order to use them to slice up curved glass display covers for the iPhone 5. This move has apparently been in an effort to accelerate production, with glass makers reportedly showing a reluctance to buy the machinery themselves due to its prohibitive cost. Lest you think this sense of urgency might accelerate the iPhone 5 from its earlier-rumored September launch, DigiTimes also reports that yields of curved glass are not yet good enough to start using said fancy machines.
At least those Cupertino designers have a couple of generations of curved iPod nano screens under their belt, giving them a good idea of how to handle the atypical glass frontage.