Reportedly, Apple's suppliers have begun manufacturing iPhone 4s with only 8GB of storage. Currently, the iPhone 4 is sold with either 16GB or 32GB of storage. As described, this seems to be a move similar to its prior moves with the iPhone 3G and 3GS, where Apple lowered the storage and sold the devices for $99 on-contract rather than the normal $199 for the lowest tier of storage.
There were rumors earlier about a lower cost iPhone, designed for emerging markets and at a prepaid price low enough to make an impact. This doesn't sound like it, however. Those rumors included a "simplified iPhone 4", one which would be carried by China Mobile (which actually doesn't carry the iPhone, yet), as well as possibly high-, mid-, and low-end iPhones which some theorized might be the iPhone 5, the iPhone 4 (downgraded storage) and the iPhone 3GS (sold free on contract and at a low price for emerging markets).
While Apple still hasn't revealed the launch date of the iPhone 5, the latest rumors have focused on late September for pre-orders and early October. Of course, no one really knows: the Cupertino, CA-based company is always secretive about new products.
We'll agree, odds are an iPhone 4 with only 8GB of storage is coming. Odds are also that it's not a significant change for Apple and will be sold at either $99 or $49, on contract.