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If I call someone at home or I have their direct line then I think "Hello" is fine. But if I'm calling a business number where it's not clear in advance that no one else would be picking that line up, I really appreciate it when people identify themselves as they answer.
I always say "Hi, this is Mary" when I answer my business line so people don't have to ask.

When I am calling someone else, I always identify myself before asking for the person.