I have an AT&T 4s with the same problem, After upgrading, whenever I attempt to connect to a wifi network I am prompted to "Login" to page that does not exist on apple's website. I've done the network settings reset and airplane mode and still am having the same problem.
Same thing here on my AT&T 4S It looks like it's sending me to some sort of Log In page on apple.com that doesn't exist. Fantastic. They need to get this fixed fast because AT&T loves to send me nastygram texts and e-mails frequently about my data usage lol.
I knew I shouldn't have updated! All of my home page apps are all there but when I scrolled over none of my apps were there!!!! I even said to myself I should wait until my iPhone 5 arrives. Oh well live & learn.