Using Dual Sim Or Usim Cards (Dual Sim Models) - Samsung SM-N975F/DS User Manual

Basics
Correct card installation (dual SIM models)
You cannot insert a nano-SIM card and a microSD card in the same place
simultaneously.

Using dual SIM or USIM cards (dual SIM models)

If you insert two SIM or USIM cards, you can have two phone numbers or service providers for
a single device.
Activating SIM or USIM cards
Launch the Settings app and tap Connections → SIM card manager. Select a SIM or USIM
card and tap the switch to activate it.
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