I just fixed this for the fourth person I know, so I think it's becoming widespread enough to warrant a post.
When using the Samsung Blackjack II on the AT&T network, you can encounter the message "403 Forbidden" when browsing to a website using Internet Explorer. Soft resets will not alleviate the problem.
A hard reset of the device, wiping it clear of everything _may_ resolve the problem, but there's the pesky issue of restoring contacts, etc.
An easier way to fix this is to open IE. Under Menu, select "Tools", then "Options". In the "Connections", check the box next to "Automatically detect settings". This should resolve the issue.
A side-effect of this fix is that you will no longer be able to access AT&T's sites while configured like this. I don't mind this a bit, as I have never found their sites useful. It is worth noting since AT&T sets your home page for you, you will receive the message "Your Internet connection is not configured properly. Please verify your settings in Connections" when you first open IE. This message does not appear for any non - AT&T sites.