What is the word for a movie or some product like a phone which is released/launched with a lot of promotion, or hype, but turns out to be very disappointing?
You could use the word anticlimactic.
This adjective could help describe the overall promotion, as well as the disappointing end to the hype.
Collins defines the word like this:
anticlimactic (adj.) (of a conclusion to a series of events, etc) disappointing or ineffective
There's also a noun form, which ODO defines as:
anticlimax (n.) a disappointing end to an exciting or impressive series of events : the rest of the journey was an anticlimax by comparison
Here's an example where one blogger used this word in a 2008 review:
Sun Introduces MySQL Tech Support for Amazon EC2 Certainly interesting, but kind of anticlimactic given the buildup from gigaom.
As another alternative, you could consider the word Edsel. Webster's defines this as:
Edsel (n.) a product, project, etc. that fails to gain public acceptance despite high expectations, costly promotional efforts, etc.
and also mentions the word's origin: the Edsel automobile produced by the Ford Motor Company.
I'm not sure if the term Edsel is used in this way widely outside the U.S., but Etymonline mentions that the word became a figurative hypernym for a "bust" not long after the car was introduced in the late 1950s. You can read a brief history of the product, including its heavy but unsuccessful marketing campaign, at this blogger's BOLDRIDE column (in case of link rot, I'll include a short excerpt):
Ford spared no expense in hyping the new model. It declared September 4, 1957 to be “E Day,” when the Edsel would be unveiled. Lead-up commercials and ads only showed partial images of the car, to create an air of mystery around it. Meanwhile, ad men told the press that the Edsel was the result of exhaustive research that had determined the “perfect” vehicle for the American people.
Unfortunately for Ford, the public didn’t see it that way. After struggling through three years of disappointing sales, the Edsel project was scrapped. The debacle cost Ford well over $4 billion in today’s money.
To this day the Edsel campaign is studied as the perfect way to NOT sell a product.
Edsel might be a particularly apt word to use if you were looking for a word to describe the product from the company's point of view, rather than the consumer's, as in:
I hope our new cell phone isn't going to be the next Edsel.