Google's cloud-based music service, Google Music, just got one of the last big-name stragglers to hop on board. According to Digital Music News, Sony Music Entertainment will makes its official announcement during a conference today, when other details will be revealed. EMI is also apparently signed on with Google Music. That means that Warner Music Group is now the only major left hanging Google out to dry. Maybe things will change after the higher-ups see the conference/announcement today? We'll see.