We recently saw evidence that the iPhone OS 4.0 is in testing, as shown by web site logs. However this week the newOSseems to be undergoing more testing, as one iPhone developer has since noted a single instance of the iPhone OS 4.0 being used in their Pinch Media Analytics.
The testing may correspond with reports of the new iPhone 4G being tested. Apple is expected to release this new hardware in the late summer months of 2010.
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Apple To Announce New iPhone At The End Of June?
Apple Testing iPhone OS 3.1.3 and 4.0