The Presto Sound Library provides a Service so that any application can change the speed and pitch of MP3s/Oggs, provided the developer of that application has modified it to use Presto and the end user has Presto installed. It is currently in open beta.
All of the documentation is in Javadoc in the Presto client. To start, you'll need to import com.aocate.media.MediaPlayer instead of android.media.MediaPlayer, and change each instance of "new MediaPlayer()" to "new MediaPlayer(Context)."