Last week, there was an announcement by Epic Games that stated Fortnite would be coming to mobile devices, with sign-ups starting March 12 for iOS users.
Sign-ups are now available via an Invite Event on iOS. Users who wish to sign up can do so here: epicgames.com/fortnite/mobile. Unfortunately, you may not receive an invite in your inbox right away, and Epic says that more users will be invited over the coming months.
Once signed up, you will receive an email confirmation:
Requirements: To participate, you need an internet connection and iOS 11 on iPhone 6S/SE, iPad Mini 4, iPad Pro, iPad Air 2, iPad 2017 devices or later. Android support coming soon.