Milk is thickly boiled and tea is prepared with a special formula of tea powder. There were allegations that bone powder used to get the thickness of the tea which gives consistency to the chai. To get the milk thickness quickly, some of them using milkmaid powder in the milk to get the consistency and slight sweetness.
The difference in Irani chai and the rest of the tea style made in India varies in the making process. The tea leaves are boiled in a separate container along with water and milk is also boiled in a separate container. Then while serving to the customers they pour in first the milk then the liquid solution made out of tea leaves. This process is seen in many places which still retain that Iranian touch. The taste of Irani chai is the same whether you go in the morning, afternoon or late evening.
Hyderabadis drink more Chai than any other state in India. I badly Miss Having 10 cups of Irani Chai per day and those funny conversations with your Mates