I remember having the same problem when I first got my 8320 Curve, and my dad having the same problem when he got his 8220. After a while of wrestling with our wireless network, we found that it was our router's permission settings. We had the wifi network set so that in order for a device to connect to the router, that device's MAC address had to be manually entered into the network via the administrator computer.
I would recommend looking at your wifi router settings and seeing if that is the case. If it is, you can find your Blackberry's MAC address by going to Settings>Status. It should say WLAN MAC and then a code. That is what you will enter into the router.
I hope this helps
8520(black), 8320(sunset), 8310(red), 8100(black), 8220(black)