Should I use my money to buy a new phone or use it to put money towards a car?

So the new EVO 3D came out today and I am over due for a phone. I have had the same phone for about a year and a half. The phone I have is very sucky and doesn't even do any thing (apps, games, etc.). With this in mind, I've been trying to save for a car. Right now I use my moms car (I'm only 17) whenever she isn't using it, but sometimes when I wanna do something I can't because she'll want it too. If I don't get a car right away I'll be fine, but it would make things a little easier. So which is it? Phone or save for a car?