Yes! This is the same problem that's bugged me for years. My thoughts

1. If you already have locked iPhone from AT&T, they can be unlocked. You don't need to buy unlocked iPhones. There're also other phones on the market which has almost all bands needed. I have unlocked phones and sims from three countries I visit most often. Because I also make a lot of local calls in these countries, math comes out ahead this way. Other countries not worth it for me.

2. If you call EU more than US, then it makes sense.

A 3rd option is if you have voip at home, and good internet connection abroad, this option will save you, not replace your current plan. Many voip providers offer soft phones. They are apps on your cell which allow you to make free calls back to any US numbers. This option only saves you if your overseas roaming cost is mostly calling US. If your overseas cell bills are mostly local calling to overseas numbers, then number 1 and 2 would make more sense.

If you're looking at getting a new phone, another thing worth entertaining is a dual sim phone. Since you travel so much, it may come in handy overseas.