Thank you for your answer, Satya!
I didn't know the "fragments" concept and, yes, the Android developers site has information about them.
http://developer.android.com/guide/topics/fundamentals/fragments.html
I hope that it let us (developers) to generate an unique UI to an application without considering where it will be executed. In other case, the effort to generate two diferents client layers probably obligue you to decide which device is the development over and, if you decide to perform that, it'll increase the maintenance efforts.
About the business layer, I'm agree with you. If the double UI is necessary, perhaps an unique business layer won't be the optimal solution.
Thank you again!