In the South East, they bring you sweetened (usually far too sweetened for my tastes) iced tea. This is amazingly universal.
I live in NC and have been probing the border for years.
For “nicer” restaurants, the universal sweet tea boundary seems to be precisely at the NC/VA border.
USA Midwest, you are generally asked if you want sweet or unsweetened black iced tea. There are usually various sweetener packets at the table that you can use. Some restaurants only have sweet tea.
This is my experience as well in the Midwest. I almost always as for unsweet and never really have a problem getting it.