Toshiba announced the lineup of products that will be displayed at its booth at SID 2011. Among those products will be a 4-inch 720p display for mobile phones. Rumors have been floating around for a while now that Apple was investing in a Toshiba-owned manufacturing facility for Retina Displays, and a 720p display on an iPhone would certainly qualify as Retina. As the press release points out, Toshiba's displays will feature other new technologies, including high-contrast (up to 1,500:1), high-color (up to 92 percent NTSC) and wide viewing angle (up to H/V 176º/176º).
However, if Apple is indeed planning on using a 4-inch display in an upcoming iPhone, it probably won't be the next one. Most of the rumors point to the fifth-generation iPhone, presumably set to debut in September, keeping the same form factor as the current iPhone 4. There's also the app scaling factor Apple would need to take into account, and devs might not be happy about having to release their apps for two different sized screens. That being said, I wouldn't be surprised to see Apple using a 4-inch 720p display in a sixth generation iPhone. Rumors have been floating around for a while now that Apple is working on an iPhone with an edge-to-edge screen, and the company could conceivably use a 4-inch display in such a device without increasing the size of the iPhone's body.