That’s exactly what your just read: the Unity3D Mobile Basic (Android and iOS), which costs $400 each, is completely FREE until April 8th. It is not a trial! Head to the Unity3D web store and download your copy.
The Unity3D Mobile Basic license allows you to develop games targeting the Android and the iOS platforms. Even though this is not a Pro license (which has lots of heavy weaponry), you still can use cutting edge technologies to create amazing games. Check this page to compare the different licenses.
Thanks Unity Technologies for that!