During the old days, there used to be a way to reach a US-based AT&T operator while traveling overseas. This was useful before the days of cell phones and prepaid SIM cards. There may still be a way to do this, but I have not tried it in probably 10 years. It may be easier to figure out how to reach a US-based operator while you are in the US and before you leave the US on your next trip.
Even for people without smartphones, you should be able to purchase a cheap unlocked flip phone in the US and purchase a prepaid SIM card at the airport of your foreign destination. Most people working at the airport will speak enough English to set up the phone for you so that you can use it to call back home.