Just in time for the impending announcement of the iPhone 5, news has come that the iPhone 4S has been surpassed as the most-bought smartphone.

Boy Genius Report cites Michael Walkley, an analyst for Canaccord Genuity, as showing that the iPhone 4S is no longer the top smartphone. Walkley’s channel checks show, as seen in the chart above, that the iPhone 4S has been surpassed in sales at two of the three major U.S. wireless carriers that sell the phone. This is to Samsung’s benefit, as the phone that appears to have taken the top sales spot is that company’s flagship Android smartphone, the Galaxy S III.

Of course, part of the reason for the slowing sales of the iPhone 4S is the nearing release of the iPhone 5. Customers are undoubtedly putting off their smartphone purchase until the end of September, and the iPhone 5 will easily top this chart in the next quarter. In fact, Apple is expected to sell an unbelievable 250 million iPhone 5 devices.

One thing that could hamper the success of the iPhone 5 is the threat by Samsung to use its LTE patents to try and obtain an injunction against selling the iPhone 5 in the U.S. Apple has drawn blood with its recent victory in the Apple vs. Samsung patent trial in the U.S., and Samsung will no doubt be using all the tools at its disposal to retain its position as Apple’s number-one competitor in the smartphone market.

(Chart courtesy Canaccord Genuity via BGR)