Jack of answers here..
what cellular provider do you have, and do they charge you exorbitantly for data use? Especially if in good coverage areas ?? Winamp! 5-bucks purchase on Google Play (if they still have it) and the internet through the phone work for this too!!
My newer car has both Bluetooth and Aux Plugin options. Bluetooth is so so, but means I must also have my cell phone plugged into charger (damned electrical vampiristic bluetooth). I will probably be getting another USB cable soon, and will either heat-shrink wrap or coil (plastic cable manager) the 6 foot audio cable and the USB power cable together as in my console/box the ports are right next to each other.
Anyway ... Winamp for android, I've never used iphones but presuming they have their itunes mobile or some other such app that should allow you to stream through the iphone's data plan.
Another option on cell phones is Spotify. 9 bucks a month though .. same for other pay as you go services (slacker, google play audio, pandora, etc) and wouldn't recommend getting one if all you're doing is getting it for the car ... 'cause in those cases, you could also just get a cheap mp3 player, and randomize all the albums you already have.
Sprint is offering that deal with Spotify ... and others have options as a monthly "add on" as if paying for it through the cellular company is anything special like you couldn't have it without them (though they generally give you unlimited bandwidth for *that* app) if you're not a cell phone glutton (more saying that for anyone else reading this) then any decent 2 gig or unlimited till X and then throttled plan, is just as good..
Personally I'm on Virgin-Mobile. 35 bucks a month, unlimited text & data, 300 minutes for phone calls. They have a 1200 minute plan for 45, and 60 is unlimited.. all are on the Sprint Network mobile backbone. Tmobile has one also, think its 40 unlimited, any option other than being in a monthly love hate relationship with the likes of Verizon or AT&T. And I live in the hills of Virginia, with a 1 hour (no traffic) commute, only in two spots along that route have I had consistent audio drop outs due to stream failure
Anyway.. for connecteds ... there's tons of tune options..
PS. Good (though some are higher bandwidth use) classical streams... "Classical 102" ' Venice Classic Radio, 1.fm All Otto's Classical, along with 1.fm's Otto's Opera, and Otto's Baroque Music.
http://www.classical102.com/
http://www.1.fm/
http://www.veniceclassicradio.eu/
And if you're into an eclectic mix every once in a while (ie non-classical music), I can't recommend RadioParadise.com strongly enough. And every once in a while Bill (Bill Goldsmith proprietor and full time music programmer) does play a piece of classical, sometimes by an alternatively known artist, and sometimes, rock pieces that have been turned into classical works simply because the guitars and amps have been replaced by cello, violin, and piano ....