9to5Mac is reporting this weekend that Apple is experiencing “atypical inventory shortages” of white 16GB iPhone 4 replacement units. As a result, it seems like [at least] some iPhone 4 users seeking hardware replacements could be in for a nice surprise.

According to the report, Apple has instructed some of its Apple Store Genius Bars to start replacing problematic white 16GB iPhone 4 models with compatible iPhone 4S units…

“This iPhone 4S would be a refurbished white iphone 4S 16GB. This situation will not affect all customers and Apple Stores, but it seems like many white iPhone 4 16GB owners seeking hardware replacements may get Siri, an A5 chip, and an eight megapixel camera out of their next Genius Bar appointment.”

It’s worth noting that this exception only applies to white 16GB iPhone 4 models that are still under their AppleCare warranties. And at this point, only Apple Stores in Canada and the United States appear to be making the exchanges.

But if you meet the above-criteria, and your iPhone 4 has been acting up, it seems like there’s a fair chance that Apple will replace it with a 4S model. Cool.

Have you received a 4S replacement for your iPhone 4?