Wi-Fi calls always originate in the US, even when you're outside of the US.
Calls to US numbers are not billed (except for 411 or other premium calls).
Calls to international numbers are billed according to your international long distance plan.
From a Home screen, tap Phone .
From the Keypad tab, enter the desired number then tap the Call icon (ubicado en la parte inferior).
Excluding the iPhone X, 'VZW Wi-Fi' appears in the upper-left of the screen.
7-digit dialing isn't supported.