How do I reduce international call costs?

Viber is working out well for me so far.
US unlimited is 59 NT per month.

I haven’t tried the Toko Indo shop calling cards, that seems like a great idea.

I tried VoIP for a bit but I would recommend against it. VoIP is easier for scammers and bots to use, so many online systems won’t accept it as a contact number, and some phone systems will block an incoming VoIP call or mark it as spam.

Personally I pay for a US number with Tello for $4.50 per month, I get unlimited texts and 100 minutes of calling (to many countries), and it’s via wifi calling/texting so I don’t have to worry about where I am.