Despite App.net's positioning as a Twitter alternative, it hasn't had either an app to call its own or a way to sign up without at least an invitation. The social network has just crossed both of those items off its list with its new App.net Passport for iOS, albeit through an unconventional path. Passport is a gateway app, not a client: it lets users manage their profiles, but it really exists to point users to third-party apps and people they'd want to follow. Don't write off Passport as a promo stunt, though. It also represents the first place where the curious can sign up without either an invitation or paying up front. CEO Dalton Caldwell warns that the wide-open registration is an experiment, not a guaranteed change in policy -- if it doesn't work out, the company may return to business as usual. Whether or not the strategy bears fruit, Passport should both serve as a fast track for newcomers and a launchpad for App.net development beyond iOS' borders.