iOS devices like the iPhone and iPad are expected to be the first to get Office Mobile around February or March, while on Android mobile Office should arrive around May 2013.
Just like current Microsoft apps on the two platforms, the mobile version of Office will require a Microsoft account. Of course, the mobile app will be a simplified version of the full Office, not the full blown package.
A Microsoft spokesperson also confirmed that "Office will work across Windows Phone, iOS and Android."
Earlier, in October, a Microsoft office in the Czech Republic mentioned Office Mobile for Android and iOS, but then Redmond denied those leaks saying it has nothing to announce.
source: The Verge