I'll do my best here, and hope I understand what you're saying. You have an AT&T locked phone, and it's not getting OS updates on another carrier, correct? If so, this is an expected behavior. AT&T pushes software updates from their servers, and in order for them to "find" a phone to update, it needs to be active on their network. If this is the care, I'm sorry, but your device will not be getting any updates unless it's connected to AT&T's network with an active AT&T SIM.
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