Huawei FLA-LX1 Guide De Démarrage Rapide page 7

Dual Card Dual Standby Single
Pass (dual-SIM devices only)
Your device supports only dual card dual standby single pass,
which means you cannot use both SIM cards for calls or data
services simultaneously.
When you are on a call using SIM card 1, SIM card 2 cannot
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be used to make or answer calls. If someone calls SIM card
2, the caller will hear a voice message similar to "The
subscriber you dialled is out of the service area" or "The
subscriber you dialled cannot be connected for the
moment, please try again later." The actual message will
vary by service provider.
When you are using SIM card 1's data service, SIM card 2's
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data service will be disabled.
Your device's single pass feature helps reduce power
consumption and increase your device's standby time. It is not
related to your service provider's network conditions.
You can go to Settings > Wireless & networks > Dual SIM
settings, and enable Enable call forwarding between SIMs
to avoid the conflicts mentioned above.
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