Unfavorable to some recent rumors, the next generation Apple iPhone 5 is coming in October instead of September. All Things Digital has heard from reliable sources familiar with the matter.

Apple has not said when it would release the next-generation iPhone, and the company is keeping everyone guessing since June’s Worldwide Developers Conference, when new iPhones are usually announced. China Times reported last week suppliers are currently preparing 400,000 trial run iPhone 5 units, set to launch sometime between September 6 and 15.

Sources with knowledge of the situation say reports claiming AT&T has blacked out employee vacations during the last two weeks of September in preparation for the retail debut of the iPhone 5 are misinformed. Instead, it’s going to be an October surprise — the month in which Apple will be launching its next generation iPhone.

As far as what the next generation iPhone will look like and the features it’ll have, we’re mostly in the dark. Some rumors indicate a small, evolutionary upgrade of the iPhone 4, while others say that the new iPhone will be thinner and have a larger display than its predecessor.

It will be interesting to see if Apple has its usual early September iPod event; surely iPhone 5 would have to be announced either before that or at the same time!