Will Apple's new iPhone see breakout sales?

It is no hidden secret that Apple is set to announce its next iPhone on Wednesday. In the past, Apple's smartphones have been a runaway success. So will this new smartphone match up to the success seen by its predecessor the iPhone 4S or will it be an even bigger success? The experts and analysts seem to have mixed thoughts in this regard.

NPD Group's Stephen Baker thinks that while iPhone 5 may be a huge success in markets across the world, it might not be the same case with sales in the United States. He points out that the new iPhone will launch in a market with very different dynamics than that of iPhone 4S launch window.

"The U.S. smartphone market appears to be an increasingly mature one. The iPhone, as well as Samsung's phones, have continued to gain brand share over the past year and their joint share now exceeds 50 percent, which is likely to make it more difficult for Apple to easily take share from weakened competitors, because many of the easy share gains have already been accomplished," Bakes shared through a blog post.

"Carrier dynamics will most certainly play into the growth potential for the new iPhone 5, as well. Last year's iPhone 4S launch could still take advantage of selling into what remained of the huge untapped base of potential subscribers at Verizon and Sprint who were not available to them previously. This year's introduction faces the specter of a much smaller base of previously unavailable consumers, based on their carrier preferences," he added.

Baker might be right, but worldwide sales have a significant part in iPhone sales number.

Fortune quizzed several analysts to find what their estimates are for the sales of the new iPhone in the first eight days and the numbers range all the way from 7 million to 12 million. These forecasts are in sharp contrast with Samsung's Galaxy S III sales, which reached the 10 million mark, in 50 days of its launch.

To provide more perspective, Apple sold more than 1 million iPhone 4S units within the first 24 hours and over 4 million in the first three days.

"Until they do something really unimpressive, which I don't see happening this time around, Apple has a serious hit on its hands," Ramon Llamas, senior research analyst at IDC told Bloomberg.

Topeka analyst Brian White too shares the same perspective about the iPhone 5 sales as he says on WSJ blog All Things Digital (ATD), "Given that the iPhone 4S received over 1 million pre-orders in the first 24 hours, we expect at least 1.3 million to 1.5 million pre-orders for the iPhone 5." He further adds, "Assuming supply chain constraints aren't a major issue and the seven country rollout ensues, we believe at least 5 million to 5.5 million iPhone 5's can be sold in the first three days."

Piper Jaffray analyst Gene Munster seems to be even more bullish in his forecast and he is expecting Apple to sell 6 to 10 million new iPhones in the first three days. He told ATD that there is no question the iPhone 5 will be the largest consumer electronics launch in history.

So, most analysts have estimated an upward of 5 million sales in weekend and upward of 8-10 million sales in the first week . However, iPhone 5 is going to be the first big hardware design change since iPhone 4, which was introduced in 2010. Consumers are expecting a lot from this new smartphone so anything below that is going to disappoint a lot of people, especially the ones who have postponed their smartphone purchase plans and are eagerly awaiting the launch of the new iPhone.

So all eyes are now set on Apple and the iPhone 5 announcement later in the day, not to mention the time when it actually goes on sale.