Use T-Mobile Wi-Fi from a foreign country to call back to a US number for no fee.

You can call at no charge using Wi-Fi calling to US numbers and also allow free sending of SMS/MMS messages. I do this constantly on “Connect by T-Mobile” a prepaid plan, also from Mint. You must following the following steps:

1. Have Wi-Fi calling set on your device, on my Google Pixel phone it on menu for T-Mobile SIM card. You might need to register your emergency location to enable Wi-Fi calling. This might have to be done on carrier(T-Mobile).
2. Be connected to Wi-Fi network
3. MUST, MUST be set to airplane mode, which will prevent T-Mobil charges (as necessary; make sure your phone is configured to allow Wi-Fi while in airplane mode, alternatively can manually reconnect Wi-Fi after going to airplane mode). T-mobile will charge you international if you are not in airplane mode, and this is costly. However T-mobile Connect prepaid does not have international travel (calling outside US), so there no chance of being charged.
   https://www.t-mobile.com/support/coverage/wi-fi-calling-from-t-mobile

Other notes:

• You can receive SMS/MMS while traveling with out charge, with out  using above procedure.
• You CANNOT try to do this through second SIM (like trying to use data on second SIM).
• You might also try setting up WhatsApp for you and your friends/family in USA, in this way you can use Wi-Fi or second SIM data, like international SIM) and also be more or less independent of carrier.