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When cellular modem interface is enabled, System LED have have alternate indications:

blinking - connection establishment in progress, modem registered in cellular network, APN is not activated yetred  - SIM card not inserted

yellow  - established connection in 3G mode

blue - established connection in LTE mode

blinking red  - SIM card not inserted- connection establishment in progress, modem registered in cellular network, APN is not activated yet

SIM slot usage

SIM card slot is designed to be used with Micro SIM cards.
Nano SIM cards have different thickness, and usage with an adapter are not recommended.

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