If you didn't sign up for the beta (or didn't yet get a code), but are in North America and still would like to join, keep an eye on their Facebook page. They have posted first-come-first-serve beta codes on there in the past, so it's possible you could get lucky.Note also that this is currently the second closed beta period (the first beta period started on January 14th). So if you missed this beta, if they do a third beta test, it's possible you'll receive a code then. If they do continue doing closed beta testing, hopefully they'll open it up to worldwide gamers the next go-around.
The currently North American exclusive closed beta period for Area 52 Games and Disney Mobile's Star Wars space combat simulator Star Wars: Attack Squadrons has been going on from January 21st and will continue to January 28th. If you already signed up for the beta, you should be receiving a code soon, if you haven't already. I just received mine, but I can't comment on the game yet, as the beta currently runs from 11AM to 9PM PST, and I entered my code a little late.