Below is a recent chat session with AT&T sales:

Scott Urman: Do you support the Treo 600 from Handspring (now PalmOne) now, and if not now, when?
Thank you for contacting AT&T Wireless. An Online Sales Representative will be with you momentarily.
[Ann - A representative has joined the session.]
Ann: Welcome to AT&T Wirelessí online web support, my name is Ann. I am reading your question and will be right with you.
Ann: We do not have that at this time. They may have those available in your local store.
Scott Urman: So you do officially support the Treo 600 now? (Although it may not be available.)
Scott Urman: Hello?
Ann: we do not have it on the web site, so I am not sure. I can look up a phone number to your local store with your zip code.
Scott Urman: Sure, 94404
Ann: 2727 El Camino Real Ste G San Mateo (650) 312-1346
Scott Urman: I'll give them a call. Thanks.
Ann: Thank you for using AT&T Wireless live chat. Have a great day!

I called the store, and they don't have any in stock, don't know when they will, don't know the price. But the guy did sound like he had been getting lots of calls about it, for what that's worth.