I've tried searching the forums to find the latest answer. Is it true you cannot have horizontal and vertical pages in the same app (project)? The app has to be either vertical or horizontal?
This is not true with AEM Mobile applications.
In AEM Mobile you can set your app orientation to "both" which will allow your user to rotate the device and the application view will modify based on device orientation.
Note that it will not force users into an orientation. So if you have built fixed-width content for a landscape view and the user does not rotate their device, they will see the content letter-boxed.
When you build your app in the apps tab, on the first page of options you'll see the heading "Device Details." There are drop downs for tablet and phone orientation there.