Are you asking how you might arrange for a european phone to be sent to an address for you here in the US?
Or are you asking how you might arrange for an unlocked european phone to be used on AT&T's network?
The first I can't comment about, the second pretty simply. You bring it in to an AT&T store and they'll spend the hour or so to set it up.
If the question is not Apple-specific, it should be moved to another forum.
If the poster wants an iPhone that can be used in Europe, he should be an unlocked iPhone at an Apple Store.
Learn how you can order the new iPad 9.7-inch with Apple Pencil Support!