Only available in the US, Blizzard has released their account authenticator as a free of charge application for iPhones and iPods.
It performs the same job as the keychain device, where a unique security-code is generated to help ensure Blizzard accounts remain unmolested. Is your Battle.net keychain secure?
Other versions of the authentication software are being developed to work on other mobiles devices reveals Blizzard Entertainment. The reason for the measure only available in the US, or at least only for US accounts, is unknown. It may have something to do with US WoW and Battle.net accounts having been merged into one.
Are you from across the pond? Do you have a fancy smancy Blizz keychain authenticator?