The big day has finally arrived, after non-stop speculation that began in January. Apple's Let's talk iPhone event is here, and there's good news for millions of hopefuls from around the world: Apple is expected to unveil the iPhone 5 as a major makeover and upgrade product from the popular iPhone 4, according to a top industry analyst.

Brian White of Ticonderoga Securities told CNET Apple's new iPhone 5 will have a sleek, aluminum unibody enclosure that more closely resembles the company's MacBook Air laptop computer than the current iPhone 4.

White agrees with popular sentiment that Apple will increase the screen size of the iPhone from 3.5 inches currently used to 4 inches or 4.5 inches. The analyst also expects Apple's new iPhone to have a dual-core processor and an 8-megapixel camera. He thinks the major upgrade will be a smash hit that will smash sales records set by Apple's iPhone 4 in the global smartphone category.

Moving into the last few months of 2011, we do not see any leading smartphone vendor that has a product powerful enough to strongly dissuade consumers from upgrading to the iPhone 5, White said. In fact, we are noticing a new wave of consumers looking forward to buying their very first iPhone this year.

Already, the iPhone is the world's bestselling smartphone, and this new model may only widen that gap, as White suggests. Late Monday, the Wall Street Journal reported that Sprint Nextel Corp. is expected to finally join AT&T and Verizon as iPhone carriers by making a multibillion-dollar gamble on the phone it hopes will turn its fortunes around.

Sprint has committed to buying at least whopping 30.5 million iPhones to sell to its customers, the newspaper reported, even though the company will likely lose money on the deal through 2014.

Apple's Let's talk iPhone event is slated to begin today at 10 a.m. Pacific Time at the company's Cupertino, Ca., headquarters. CEO Tim Cook is expected to preside, and the company is also expected to unveil a new iPhone 4S, lower-priced than the iPhone 5, among other new products and features.