Just thought I'd add that Spotify is now offering 6 months of free unlimited music after which you either become a paid subscriber or are kicked to an ad supported version with a 10 hour a month limit.
I am not sure however if the free 6 months includes the ability to stream from your smartphones.
Being a paid subscriber myself, I can say that Spotify is awesome. The phone app can be buggy, but it's still relatively new. I'm sure once it's been revised a few times it should only get better. $10 a month is a pittance if you buy music on the regular. Just add a new playlist each month. If Spotify were to charge me for all the music I have set up on my account, I would owe them 26 years of subscription fees.
Be warned, there are artists and labels that have still yet to reach a deal with spotify. So be sure to search their catalog beforehand. My personal music tastes made me go with Spotify over MOG, Rhapsody, etc..