长时间不见怎么问候：It's been very long since I met you last time.

电话中怎么问候：Hello, this is [你自己的名字] speaking. Can I talk to [要找的通话方的名字]？

平常遇见怎么问候：Hi!（最简单的）；How do you do?（比较文雅的）。

第一次见怎么问候：I am very glad to have chance to meet you；I am very glad to make your acquaintance