Previously, Electronic Art’s Tetris has been available as a $2.99 downloadable game, but similar to what we see with Angry Birds, a free version of the game is made possible thanks to its support of ads. Of course, you might be bombarded by some sort of advertisement as you’re sweating away trying to keep up with the falling blocks. Still, it’s just one distraction you’ll need to endure to play this classic game for free.
Still, if it’s too obtrusive for your tastes, then we’d suggest forking out that $3 to purchase the ad-free version of the game. However, it's very hard to not like that free price tag.
source: Android Market via Android Central