Wal-Mart confirmed Friday what everyone who follows Apple already knew: that it will begin selling Apple's iPhone 3G at nearly 2,500 Wal-Mart stores starting Sunday Dec. 28 — three days after Christmas.

Wal-Mart will sell the red-hot mobile device for $197 for the 8GB model and $297 for the 16GB model, or $2 off their current prices. There had been rumors that Wal-Mart would sell a $99 iPhone. (See Anatomy of a rumor: Wal-Mart's $99 iPhone.)

Wal-Mart, however, appears to be giving individual store managers some wiggle room on prices. According to the press release, the company's price match policy will allow stores to "match the price of any local competitor's advertised store price on the same item within the same promotional period." Best Buy is offering the iPhone for $190 for the 8GB and $290 for the 16GB models.

Getting the iPhone into Wal-Mart (WMT) is something of a coup for Apple (AAPL). Wal-Mart is the world’s largest retail chain — by far — with more than 7,000 mega-stores around the world and some 2.1 million employees. It finished its last fiscal year with nearly $380 billion in sales — earning it the No. 1 slot in the Fortune 500.

The move represents the fourth major expansion of the iPhone’s retail presence outside Apple’s own 200-plus stores. The phone was sold first at AT&T’s (T) 2,000 retail outlets, then at nearly 1,000 Best Buy (BBY) outlets (see here), and then at the tens of thousands of points of sale (many of them no more than mom-and-pop kiosks) that carry iPhones for Apple’s overseas partners.

Piper Jaffray’s Gene Munster has estimated that Apple could easily sell as many iPhones through Wal-Mart stores in 2009 as it sells through its own Apple Stores — by his calculation, about 4.5 million units. See here.

The blogs and business wires were buzzing Monday morning with two juicy iPhone rumors: 1) That Wal-Mart would begin selling iPhones three days after Christmas and 2) That a low-end model would sell for $99.

The first, as we reported nearly three weeks ago, is true. (See Wal-Mart's post-Christmas iPhone sale.)

The second, as near as anyone can tell, is almost certainly not true – although it seems to have taken on a life of its own, most prominently in a Bloomberg.com report published Sunday evening.

On Monday morning, MacRumors reported that, based on leaked Wal-Mart training and advertising material, the $99 iPhone rumor was "unlikely." MacBlogz went further: "Based on every piece of information we’ve heard, and direct information inside AT&T, this is not happening."

So how did the story get rolling?

It started with the Boy Genius Report. a blog with back-channel contacts at AT&T  (T) that have often proved reliable. In fact, the news that Wal-Mart (WMT) would be selling Apple's (AAPL) iPhone originated with Boy Genius, although the date that sales would begin was fuzzy until a Boy Genius reporter got his hands on an AT&T memo spelling out the timeline for in-store training  and national rollout. (link)

The $99 iPhone rumor, although originating from the same site, had a very different feel to it. The Boy Genius report posted on Dec. 4, started like this:

"We just got a tip that in addition to the iPhone 3G actually making its way to Walmart, as we exclusively told you, there will be a 4GB model priced at $99 with a 2-year agreement. We’re not putting our stamp of approval behind this one just yet as the tipster isn’t listed in our BGR’s Guide to respected Ninjas handbook, but it does make you think, doesn’t it?" (link)

The $99 rumor got conflated with the Wal-Mart story in subsequent reports — after all, they both came from the same blog, right? — and received what was taken by some as confirmation when Shaw Wu, an analyst who follows Apple for Kaufman Bros., addressed it in a report to clients:

"While we are not sure of exact timing, we think a $99 Apple-branded cell phone is inevitable." (link)

Wu's remarks were picked up by Bloomberg's Connie Guglielmo, and by Monday they had made their way to the top of the online news food chain at Techmeme.com.

In fact, the iPhones at Wal-Mart will be sold at a discount, as VentureBeat reports and the ads leaked on MacRumor confirm: for $197  –  $2 off the $199 list price.

The Boy Genius, for his part, hasn't backed off his initial report, but neither is he fully endorsing it. "Waiting for some feedback from a couple sources," he wrote in reply to an e-mail inquiry. "At this point I just don't know."

Neither Apple nor Wal-Mart would comment on the rumors.