honor BND-L21 Guide De Démarrage Rapide page 7

Dual card dual standby single pass
Your device supports only dual card dual standby single pass,
which means you cannot use both SIM cards for calls or data
services simultaneously.
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When you are on a call using SIM card 1, SIM card 2 cannot
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 dialed is out of the service area" or "The
subscriber you dialed 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
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.
It may be a good idea to contact your service provider and
subscribe to missed call reminder and related assistance services
to avoid the conflicts mentioned above.
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