Looks like the mobile authenticator is now available for iPhones, iPads and iPod Touches. Here is what you do after you download the free app from iTunes.
https://www.riftgame.com/en/products/authenticator.php
Please note that the random number generated by the iPhone or iPod Touch (or Android phone) changes rapidly. You only have a short amount of time to type in the letters/numbers before it changes to something else, which can be rough on folks with physical impairments.
UPDATE: Here's a detailed essay on protecting yourself as a gamer from hackers.
http://www.riftsocial.com/prevent-hacking
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