Kivy is a solution for developing smartphone applications in Python without spending too much time managing platform differences. For many reasons, it is very popular and manages to remain very Pythonic. It has just begun the process of migrating to Python 3.
Here is the link to the essential part of the site, the documentation: http://kivy.org/docs/.
It is not yet fully complete, but there is already enough to get started, with access to the API, source code, and testing capabilities.
Personally, I have been looking for a solution for this particular development niche for some time, and I think I have found it. I was planning to start testing in February 2013, but the Kivy community has begun the process of porting to Python 3. So I am eager to see what happens in the coming months.
The port would cover Kivy itself, but also some of its dependencies like PIL, gstreamer, or opencv, which are very important, even reference modules.
The same news also mentions NLTK, another project carrying out its port. As a reminder, here is the porting status of major modules to Python 3: http://python3wos.appspot.com/.