Simplify the only music streaming software that I would ever use for my iPhone.  Simplify allows you to access all of your iTunes music over any wifi connection.  You can acess up to 30 computers with one registration.  The best part is registration is FREE.  I have been using Simplify for about 2 weeks now and all I can say is wow.  The software on the phone while a little glitchy works very well.  I rarely hit buffering spots in the songs as most songs just download completly to a cache.  The songs continue to play while you are on the home screen so you can still use all of the phones features.  The software of course also gives you the option to buy the song on iTunes.  All in all its an amazing free program for unlimited access to music.  For more information visit http://www.simplifymedia.com/.