How to choose a SIM card for outgoing calls?

If your Android device has two SIM cards installed, NumBuster allows you to configure the phone number selection for outgoing calls.

Make sure Full-screen Caller ID mode is active in NumBuster. You can learn how to set up full-screen mode here.
Tap Settings and go to section Calls & Widgets.
Tap Number for calls and select a SIM card or the Always ask option in the pop-up window.

Selecting the Always ask option will show a request to choose a SIM card whenever you make a call.