I just got an iPhone and I've already used a ton of data?

I'm on a 2gb data plan and I only got 2 because I have Wi-Fi at home. Even though I have the Wi-Fi, even when my phone is idle, it is still using up my data. I don't know what is going on with it but is there any way to get this under control or some kind of app to help out with this?

Added (1). Thank you Sora! That sounds like the best thing I could do. Now this is my first smart phone so I still have so much to learn about this.

You can always go to settings-general and disable cellular data, this means it will compeltely turn of the 3g. Or if you are jailbroken, get sbs settings and there should be an option to disable 3g

  • Will downloading a ton of apps and then deleting them slow your iphone down? If i download a ton of apps and then delete them in order to get rewards points for apps for free itunes money. Will that slow down my iphone or affect it in any way possibly?
  • Syncing device with TON of music, what'll happen? So I have an IPod touch with a lot of my music and all I want to do is put it (music) on my computer so I can than download it to my new iPhone but I read somewhere that if you sync a device with music the music is erased and that Can't HAPPEN! Please tell me what would happen and how I can prevent delete-ery
  • Just cracked my iPhone 5 (just got 2 weeks ago)? Like in the title just cracked the screen and wondering what my next step is? Some say its a free replacement since I just got it. Replacement at the apple store, but I know th warranty doesn't cover this since it is an accidental damage. Very confused and so pissed if I have to pay for a brand new one this is just a few weeks brand new.
  • I want the iPhone 5s or 6 so bad, but I don't want to pay a ton of money? I currently have the iPhone 4 from Virgin Mobile and am only paying 35 dollars a month. I want the 5s or six so bad, but I don't want to pay full price for it and no more than 60 dollars a month for a plan. What should I do? Please help! (My 35 dollar a month plan comes with 300 minutes, unlimited text and data)