Apple's marketing copy on the term specifically says: "the Retina display’s pixel density is so high, your eye is unable to distinguish individual pixels."
It isn't tied to a specific PPI number.
And besides, depending on how good your eyesight is, the iPhone 4 'Retina display' moniker can be bogus, anyway (http://blogs.discovermagazine.com/badastronomy/2010/06/10/re...)
Apple's marketing copy on the term specifically says: "the Retina display’s pixel density is so high, your eye is unable to distinguish individual pixels."
It isn't tied to a specific PPI number.
And besides, depending on how good your eyesight is, the iPhone 4 'Retina display' moniker can be bogus, anyway (http://blogs.discovermagazine.com/badastronomy/2010/06/10/re...)