With ATT, nothing is free, especially internationally. When we had ATT wireless, we put our phones into airplane mode (no cellular phone calls) & then turned wifi back on. You do NOT want to use any public wifi! Instead, we've rented a pocket MiFi from various European companies, depending on where we were going to travel. One of these companies we would rent again from is Hippocketwifi.com. The device is typically waiting for you at your first hotel & includes a drop envelope that you leave with your last hotel or mail from the airport. It converts local cellular to wifi, supports up to 5 devices, is affordable, portable (the size of a cellphone or battery pack), is rechargeable, and most important, is password secure. You typically choose a total amount of data which can be topped up if you need more. We limit our usage to email, GPS, making reservations, & downloading kindle books.
We now have T-mobile's senior plan (one person must be 55+): 2 devices for $70/month, including all taxes. This is unlimited data, calling, & texting in the USA -- way cheaper than ATT. We've not had one dropped call, which was happening frequently in our Austin area house. It detects & alerts scam calls. Some access to Mexico & Canada. We haven't traveled internationally with it yet, but T-mobile advertises unlimited text and data included in the plan. VOIP (voice over internet) works if your phone supports it.