Galaxy J2 Core: How to activate Smart Dual SIM?
Smart Dual SIM enables call waiting on both the SIM cards. It even enables the call forwarding on both the numbers. So, if one of the numbers is out of reach, the incoming calls will be forwarded to other number.
Navigate to Apps → Settings → SIM card manager → Smart dual SIM → Enter both SIM card Numbers → Next → Finish → Ok
Pictorial representation to activate Smart Dual SIM is as follows:
Setting preferred SIM or USIM cards : When two cards are activated, you can assign voice calls, messaging, and data services to specific cards.
Launch the Settings app, tap Connections → SIM card manager, and then set the feature preferences for your cards in PREFERRED SIM CARD