Is your device Factory unlocked with a model number ending in U1? If not then it is carrier locked, to AT&T and is ineligible for the beta, so the banner will not appear.
I was unable to participate in the Beta 1 release due to the enrollment list being full. However, persistent attempts at six-hour intervals resulted in successful enrollment two days later at 6:01 AM EST. This suggests a possible daily enrollment limit. Furthermore, anecdotal evidence suggests that using an unlocked device, and those from T-Mobile, may increase enrollment success. This is likely because postpaid carrier contracts place warranty/support responsibility on the carrier in the event of beta software issues.
I've been asking around all day with the same question. I was "approved" late last night and since then I've searched everywhere for a link or something to download and get nothing.
