There is an iTunes app (not compatible with ipod touch 4th gen btw) that allows you to unlock new skins for Injustice HERE which takes a very long time to unlock everything. A member of GameFAQs is sharing his WBID with everything from the iOS app unlocked. If you wish to use it.
Login:frankzurick@hotmail.com
Password:redson
If you linked your WBID in Gotham City Imposters to your Xbox, you will have to unlink the account in that game to get the skins in the new game.
If you want to unlock them yourself here is some info:
http://www.ign.com/wikis/injustice-gods-among-us/Secrets_and_Unlockables
http://www.justpushstart.com/2013/04/how-to-instantly-unlock-every-ios-unlock-in-injustice-gods-among-us/
http://www.gamefront.com/injustice-gods-among-us-ios-app-console-unlockables-list/
