Of all the games for the iPhone, this is in my top five for ingenuity.  In it, you are essentially playing jumble to find the most words possible with a given set of letters.  You submit words and find new ones as fast as possible. 

If you register you can chat with other people playing at the same time and see their scores.  Frozen Lexicon is a fun, smart game that it absolutely worth playing.  

The site instructions say:

Spell words to score points. Spell one six letter word to keep your score for the next round. Your score progresses until you fail to spell a six letter word. A marks a bonus word.