Next Generation iPhone being tested in the field?

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MacRumors is reporting on a tip they received from an iPhone app developer. The developer of iBart, a program for the trains in San Fransisco, noticed that one of the phones being used to access the iBart service is labelled the iPhone 3.1. The newest iPhone 3GS is only labelled iPhone 2.1.

Now it is not unheard of for Apple to let their prototypes into the wild for testing, sometimes even far in advance. For example, the iPhone 3GS was tested in the wild as early as 8 months before. So while this doesn't tell us anything about an immediate release, it does hint at an iPhone refresh in the usual July time period.