“The new iPhone just came out, and I've GOT to have it.”
You want to buy a new phone and you're explaining why to your wife. You say this in excitement.
The new iPhone just came out, and I've GOT to have it.
Why does the speaker say "the new iPhone" instead of "a new iPhone"? It's because everyone expected a new iPhone to be introduced around this time. If you think your listeners know what you're talking about, you should use "the".
Use the phrase "the new ___" when talking about new products that have been eagerly expected. For example:
Have you heard the new Katy Perry album?
I can't wait for the new Harry Potter movie.
When a product starts to be sold, you say that it "came out". Use this to talk about electronics, books, movies, and so on.
I remember when the Playstation first came out, it was the most awesome video game system I had ever seen.
The Lost Season 6 DVD is coming out in a couple weeks.
After something "comes out", you can then say that it is out:
Is the new Will Ferrell movie out yet?
It's been out for a few weeks.
This is a phrase in casual English that you say when you really want something. When you express what you want in this way, you sound a little like an impatient teenager.