This depends on the context.
In person in a small group, you'd say "Hi! I'm James!" and probably extend your hand to shake.
If you are in front a of a room of strangers introducing yourself, you might be more formal, with "My name is James".
However, if you're joining a conference call, you'd say "Hi! This is James." That's because you expect that the people you are talking to probably know who you are, or at least could look at the list of invitees, but they don't necessarily know that this voice is yours.
"Hello, this is James" was also a common way for someone named James to answer the phone, back in the days when phones were more tied to a location than individual devices as mobiles are today.
1This is a man - perfectly ok. – mplungjan – 2017-12-01T06:29:02.073
This, that, these, those and other related expressions are fine for people. It is not (normally) appropriate for people. – Andrew – 2017-12-01T08:15:22.323
3@Andrew However, "it" may be appropriate in this case. "Hi, it's James" is quite common in informal conversation, especially on the phone – georgewatson – 2017-12-01T08:47:26.510
13Introducing oneself as "Hello, this is X" (such as on the phone) implies you are already known. In short, it's not so much introducing oneself (adding a new name to someone's list of known persons) as identifying oneself (help someone know which persone on the list is speaking). – Medinoc – 2017-12-01T09:48:47.053
@georgewatson Yes, that's right. That's the existential "it" but still that is kind of weird and inconsistent. Oh well, I guess that's English for you. :) – Andrew – 2017-12-01T15:53:27.130
2
Possible duplicate of A: Is it wrong for John to say “This is John”?, although at least two of the answers here are very good.
– green_ideas – 2017-12-01T16:16:43.6071@Medinoc Saying "This is X" or "It's X [here]", usually only happens when the speakers can't see each other, e.g. on the phone or at the door. It's not just when the speaker is already known, e.g. "This is X from company Y calling." (a stranger). It's also often preceded by "Who's that?", "Who is it?", or even just "Hello?" – CJ Dennis – 2017-12-02T03:48:57.763
Thank you Guys. I would have loved to accept both answers, but I can accept only one. So I chose the one looks concise. Expecting to learn from all of you. I am trying to be a good English Teacher leaving my IT background behind. – Jamess – 2017-12-02T08:32:23.833
So it looks like newer form of conversation such as one in a youtube video, may be "This is .." accepted like on phone call. – Jamess – 2017-12-04T13:48:00.407
@Andrew an Interesting, but confusing point you made that "This, that, these, those and other related expressions are fine for people. It is not (normally) appropriate for people". Sorry, I did not get the difference between fine vs appropriate in this context. Can you please explain with an example ? Or Does that warrants another independent question ;) ? – Jamess – 2017-12-04T13:49:36.433