While on a call with at&t BlackBerry support, I was told the 8310 was due shortly. But the gentleman said they had been testing the 8320 and found some "issues" with it. No, he didn't elaborate on the issues. But he said that one would not be coming out anytime soon.
Personally, I love the 8820. My company tried to force me to a Curve. I'm still on the 8820.
I do wish at&t would support the Voice over WiFi options like T-mobile. I just seem to wind up in too many conference rooms with no cell coverage and still good WiFi signal. :(