You have ample choices when it comes to music streaming on Android, and SomaFM has been among them for a long time. However, it's always been a paid app. Now, it's suddenly free, and in the Play Store, that means it's free forever. It's not clear what this means for SomaFM's business model, but hey, free stuff is cool.
SomaFM streams indie tracks and a lot of electronic stuff. If that's something you're into, you might as well check it out. It's also part of T-Mobile's Music Freedom, so it won't count against your data cap. The app has bounced around a bit in price, most recently costing $3.99. It's not exactly the prettiest app, though.
SomaFM and other small streaming services are currently stressing about the expiration of a deal that streamlined royalty payments for streaming. In 2009, the Copyright Royalty Board decided that streamers could just pay a percentage of revenue instead of a per-stream fee to copyright owners (you might recall Pandora had a blackout day to garner support for this deal). That agreement is expired now, and SomaFM has been tweeting about it a lot.
Presumably the price drop and royalty changes are related. SomaFM has never relied on ads for revenue in the past, but the move to free indicates the company will have to do something to make money.