Developers have been seeded the new iPhone 2.1 Beta 4. Apparently it is missing the push notification service. Apple says that they are further developing the module in parallel.
The service was announced already at the WWDC and should be available fully in September.
The push notification service is important for all message related applications that would be able to receive updates from servers when running in the background. More details on MacRumors.
Back in July Apple started to seed beta versions of the next major iPhone OS update.
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