The migration tool is available right on the Moto Maker. After you've built your custom Motorola Moto X, you will see an invitation to Migrate. Once you accept the invite, you select "I have an iPhone" and enter your AppleID and iCloud password. Hit Continue and Begin Transfer, sign in to your Google account and the migration will begin.
Making it easier to migrate from the iPhone to the Moto X could help Motorola and Google grab some business away from Apple.
Migrating from iOS to Moto X
source: Motorola, +PunitSoni via GigaOM