Besides AT&T and Apple Stores the iPhone 3G is already sold at electronics retailer Best Buy. Now BoyGeniusReport quotes sources saying that Walmart is supposed to start selling the iPhone 3G starting November 15th.
The Apple iPhone 3G is the 2nd best selling mobile phone in the United States. It makes sense for Walmart to carry this "mass market" product. Wal-mart of course already sells the Motorola RAZR V3, which is top selling phone in the States.
The rumored sales launch of the iPhone 3G at Walmart is very close to the Thanksgiving and Black Friday sales explosion. If Walmart cuts their margins and contract signing fees a bit they could put a special Black Friday sales offer on the iPhone 3G, which could result in a stampede in their stores.