I've been a tea drinker (hot and iced) all my life. I was introduced to Chai tea at a local bagel shop and it's my new favorite. I found the concentrate at the local food coop for $4.44/pint. It's made by Oregon Chai Tea company and I think it's much better than the other pre-mixed you might find.
I've also brewed the tea and added milk, but the concentrate makes a tastier cup. Regarding it's similarity to Thai iced tea - the Thai recipe calls for coconut milk or sweetened condensed milk, but Chai tea can be mixed with your choice of soy milk, whole or non-fat