There are 3 major methods of producing "iced tea."
1) Steep extra strong in hot water, pour over ice.
2) Sun Tea, where you take a large gallon size mason jar (or stylized sun tea jar), put the tea infuser (or bags) inside, top up with icy cold water, then set in the sun.
3) Ice-brewed ice tea/refrigerator tea, where you place the infuser directly into ice water, cover, and keep cold until it steeps out.
Method 1 activates the flavinols found in tea in the same manner that normal hot teas do. However, it also released the tannins, which then have a tendency to oxidize after being chilled, making a nasty bitter taste, (and if allowed to sit, will manifest as an oily looking sheen on the top of the tea. Blech) This method ONLY works with tea that is brewed right on the spot, poured over ice, stirred up vigorously, and then IMMEDIATELY served.
Method 2, as pointed out previously-- is often incorrectly done. Done properly, it produces a dark colored but very mild tasting tea.
Method 3 likewise produces a very mild tasting tea, and is harder to screw up. However, there are some pitfalls, as pointed out previously. The use of plastic pitchers is very common these days, and it affects the quality of the tea by harboring tannin deposition via capillary action. It makes dirty looking pitchers very quickly that are hard to clean, because oxidized tannins become insoluble. (that's why they make an oily sheen on old tea). People also often forget to cover the tea pitcher, and refrigerator flavor can get into the tea. (blech)
Try to avoid metal tea infusers. They are very prevalent, but they do react with the tea a little, and can throw off the flavor. Glass is best.
Iced tea is intended to be a large tumbler full / tall glass type drink for hot days. As such, it is usually served basically universally in that fashion; big pitcher of tea, tall glasses, sugar and lemon on the side.
This is contrast to the multitudinous ways that hot tea is served, especially in the UK-- where tea is mostly a hot drink for chilly days (which is basically always.)
In the deep south, this is offset with other kinds of tea, that arent made of black tea leaves. (Heresy in the UK.) Things like mint tea, chamomile tea, and the like are commonplace.