you can read separate when you mean somethings such as room number or phone nymber.For instance,you say"我的房间号是五二一九”. If you want to emphasize the quantity of something you read with together.For instance,you say"我有五千二百十九元钱“. 谢谢！

Let me give you some examples. 1.One number:6——六 2.Two numbers:16——十六 26——二十六 3.Three numbers:106——一百零六 156——一百五十六 4.Four numbers:1006——一千零六 1236——一千二百三十六 5219——五千二百十九 5.Five numbers:10006——一万零六 14560——一万四千五百六十