We don't have confirmation on this beyond the word of a Czech-based developer who has tested it, but apparently Apple is blocking push notification services in unofficially unlocked iPhones. However, we have tested it and it works.

The developer says the following:

According to technical documentation, every Push application has to request the unique token from the Apple's APNS servers to identify the device it's running on. Thanks to that token, APNS servers always know which device is yours. The token can be understood as an IP address — the server has to know where to send the notification ...

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