Apple's online stores ran dry of the low-end 8 GB iPhone 3G several weeks ago, with AT&T following suit late last week.
Apple's clearance prices on iPhone 3GS models may not be the best deal available, however, as Wal-Mart dropped the 16 GB model to $97 late last month. It is not entirely clear what Wal-Mart's plans are for clearing any remaining stock and bringing in the iPhone 4 are now that an official launch announcement has been made.
For its part, Apple will be maintaing its own $99 price point previously held by the 8 GB iPhone 3G by releasing a new iPhone 3GS similarly carrying only 8 GB of storage. While Apple almost certainly could have squeezed in 16 GB of storage at that price point, it elected not to do so, presumably to maintain differentiation from iPhone 4.