Not sure if this qualifies as a 'mobile game' but has anyone tried 'Say the Same Thing'? It's a cool idea for a game (not just a mobile one, seems like it would be good for dinner parties or something) that apparently was thought up by Ok Go (the band).
Basically you and another person (friend or anonymous) both say a random word at the same time, and then when you see those two words, you have to then both say a word in between them, in order to try and get you both saying the same word (hence the name!).
It's quite hard at first, but reasonably fun.