If you want hot tea in an American restaurant, that's what you're going to have to ask for - "hot tea". Otherwise, the server will assume you mean ice tea, and then it's just a question of whether you want it sweet or unsweetened. As others have said, ordering hot tea will likely just yield you a small metal teapot and a single bag of generic black tea, most likely orange pekoe. Places specializing in hot tea are not common in the US. Mostly they're a thing of metropolitan areas with large enough Asian populations to have an ethnic enclave section of the city (i.e. Chinatown, Little Seol, etc.). I do think hot tea is slowly becoming more widespread here in the US, but it's still uncommon.
Personal rant: I abhor sweet (cold) tea. Honey is fine in hot tea, especially herbal teas, but ice tea is a Southern perversion. Up until about maybe 8-10 years ago, you didn't have to worry about sweet tea unless you crossed the Mason-Dixon line. Past it, you automatically got sweet tea if you asked for tea, and asking for unsweet tea made you a social pariah on the order of someone who orders their steak well done.
North of the line, restaurants kept sugar out for the oddballs who wanted to add sugar to their tea (or coffee). This was fine, and socially acceptable. I was personally happy with this status quo. I never got blindsided with sweet tea, and if I was traveling in the south, I knew what to expect, and adapted accordingly.
However, sweet tea has become pervasive across the US. Even in my homeland, I now have to specify unsweetened tea. Interestingly enough, with the spread of sweet tea into new territory, I've noticed some vocabulary distinctions that have become common. It's now very common to order "ice tea" if you want sweet tea, and "sweet tea" if you want it sugary. It's an odd distinction, because of course they're both served cold with ice. I think this is likely because it's so hard to differentiate "sweet" and "unsweet", especially when ordering over drive-through speakers of dubious audio quality. I got tired of intentionally over-vocalizing my "UN", and have mostly had success just using "iced".
I don't know who to blame, aside from the American consumer, but I attribute it to laziness and people who can't even be bothered to sweeten their own damn tea. It's less and less common to see sugar out on tables now, as well, which I suppose is a direct correlation. I guess those who want it in their coffee have to ask, but who cares about them.
I'm just a little miffed because if I wanted to stem the tide of sweetened tea, I would just live in the southern US. I shouldn't have to deal with it in the high-plains.
