It cannot be used to mean hello outside of a phone conversation, however.
It’s placed in front of the verb that it modifies:
He just left. He has just left.
Study notes:
This is often used to give one’s advice or opinion based on a conditional.
If it's you (we are talking about), you can do it.
Examples:
A Japanese person wouldn't do such a thing.
If you have to get work done, hurry up and do it.
If I like the flower, I'll buy it.
I want to go there someday.
I want to go there again someday.
I want to go to Japan someday.
I couldn't sleep.
I couldn't sleep at all.
I never closed my eyes all night.
Go and wake your brother.
I awoke from a dream.
Call me early.
Don't forget to call me tomorrow.
I can't conceive how you can sleep so long.
China itself is no longer keeping its distance from its fellow-Chinese who have chosen to make their living abroad, and it is possible that this new, more diplomatic face of China will become openly influential, perhaps even hegemonic.