This is from the blog that I follow:

First of all, you have to understand a distinct difference between the North and the South.
If you're in the south, and you order a drink of water, there's a pretty good chance of ice cubes in it. The pitchers carried by waiters and waitresses often have a special side 'spout' that is designed to pour ice from the pitcher to the cup.
I have been told that if I order a drink in the north, it comes 'straight up', aka without ice.
This makes sense - it's generally colder the farther north you go (in the Northern Hemisphere, of course), so there's little need for ice, the opposite being true as you travel south. Apparently the Mason-Dixon line is the Ice Equator as well.
When in Texas (unless you find a restaurant trying to reserve resources, which generally warns you ahead of time), you will get ice in pretty much anything but milk and some kinds of juice.
You can of course ask for a drink without, but bear in mind that if you don't, it'll come on the rocks.

BACK to my initial subject; while we do in fact have 'gourmet' (as the grocery stores will tout it) teas, that is, things like Earl Grey, available, you should keep in mind that just because they say that does NOT mean that an English tourist will agree. But I'm talking about normal tea, Lipton packets etc. etc.
To some, the idea of 'iced tea' (which is pretty much tea on the rocks) is completely out of left field. To those of us used to 105-degree-in-the-shade springs, it is not.
There are two basic ways to get ice tea. One is to, of course, brew up a bunch of tea bags in hot water, allow to cool, and then drop a truckload of ice into it. The other way is to use special tea bags, designed to be used in cold water. However, this has a different taste than normal tea.
It's far more common to get ice(d) tea in a southern restaurant; if you want it hot, you have to specify. Most sit-down restaurants, the nice ones at least, have the option of 'hot tea' (yes, that is what you'll have to ask for!), and many have more than one flavor available. However, I wouldn't recommend it, unless it's winter or you get cold easily.

Another standard to keep in mind - and watch out for - is sweet tea. For those who are big on specific language, this'll drive you crazy - plain tea, without sugar, is almost universally referred to as 'unsweet' down here.
Sweet tea is almost definitely made so with white sugar. However, the usual rainbow-colored sugar substitutes are available in almost every restaurant, including (although much less so) Splenda. If you have dietary concerns, or simply do not like sugar, it's best to order the tea 'unsweet', and then flavor as you so choose. If you order in a restaurant without specifying, it tends to be a toss-up, so WATCH OUT!
Also keep in mind that everybody has their own opinions on sweetness. Some believe sweet tea should be impossible to move a spoon through, others prefer a more moderate taste. If you're filling a cup at an open soda fountain, which down here almost always have tea, it's a good idea to pour in just a little and then sip, to make sure the sweetness is alright.

There are a variety of specialty cold teas, many of which are worth at least one try. If you find yourself in the South, have a taste; in fact, it'll probably be preferable, considering the likely weather.

I'm excited because I am heading down to Texas for a short stay, and I will keep all of this advice in mind when ordering up. I'm really looking forward to the visit; us cowgirls love Texas :)