Not sure but just read this review from PC Magazine:
Don't expect Wi-Fi to greatly speed up Web browsing or e-mail. As I found on the 8820, the BlackBerry system is so optimized for slow networks that there's very little visible difference in the speed of Web page loading in the BlackBerry browser or e-mail delivery over Wi-Fi versus EDGE. Browsing, IM, and other Internet applications all work over Wi-Fi, no problem—they just don't work much faster than they did before.
Wi-Fi does seem to take one toll on the Curve 8320: It is generally a touch less responsive than AT&T's non–Wi-Fi model, with menu options taking a little longer to register. It still feels livelier than Windows Mobile, though.