If you've been waiting to get your hands on an iPhone 3G, be prepared to keep waiting. AT&T only takes advance orders, and Apple stores are sold out across the country. You've got two options: go through AT&T's direct fulfillment plan and be patient, or keep an eye on which stores have the iPhone in stock and
get camp there as early as possible. The 5th Avenue store here in New York City had iPhone units in today, but they also had a five hour line, and there certaintly aren't enough phones to go around.
How will you know when the iPhone 3G is back in? Apple is making sure the word gets out only through its site and stores. iPhone availability tracking sites outside of Apple such as TopMuffin have found themselves cut off from the company's stock numbers. A prospective iPhone buyer's most reliable recourse is to give the nearest Apple store a ring or check Apple's website after 9 o'clock at night (wherever you are), for the following day's availability.
And that's how it looks right now, folks. Pay in advance and wait for AT&T to call you to pick up your phone, or keep an eye on Apple and take your chance in line.