Some free phone applications that test and improve the user's vocabulary are Letris 4 and Textropolis. Both of these applications use games, levels and challenges to keep the user entertained while learning.
Letris 4 challenges the reader to keep as much of the screen clear as possible by building words with the provided letters. The application and dictionary are available in a variety of languages other than English, and there are 300 free levels in the history mode. In Textropolis, a user builds his vocabulary by playing through 30 cities in a game of word discovery. Each city grows with the more words the user discovers.