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.
In Vietnam, if it’s a café they’d ask you hot or cold.
Normal restaurants you’d get iced tea, usually very strong unsweetened Lipton yellow label.