Iphone 4- bought an unlimited data plan but it says I need Wi-Fi for facetime?

I should just be able to use the 3G right? Why would I need Wi-Fi? That's the reason we bought an unlimited data plan; so that we wouldn't need Wi-Fi. The internet, however, works just fine, other than being a little bit slow, but it connects to the internet and app store just fine without Wi-Fi. It only happens when I'm trying to run apps like snapchat or trying to use facetime. Why is this?

Additional information- I have cellular set to on in my settings. I have Wi-Fi turned off in my settings. I just got this phone yesterday and I've never had an iphone before so is there something I didn't set up?

Added (1). My family and I didn't spend any money on it. It was free as an upgrade. And they surprised me with it. So next time don't make assumptions. And as I said before, I've never had an Iphone before so how was I supposed to know. If I had paid for it, I would have done research.

How to transfer music from an ipod to an iphone?

I just got an iphone, so how do i transfer all the music (and apps?) from my old ipod to my new iphone?
Is there a way to transfer pictures?
its an ipod 2nd generation and the iphone is an iphone 4

Why does my iPhone 4S drain extremely fast when 4G is turned on?

I always keep my 4G data off because if I leave it on, I'll lose a large percentage of my battery. Why is this? I use AT&T. How do I make my battery not drain? Its a huge difference between the rate my battery drains when you compare it to when I only have Wi-Fi on.

When I send pictures from my IPhone, does it use data?

I just got a new IPhone and I went from a dummy phone. Since I don't have a data plan I was wondering of sending pictures requires data… I don't have a plan but I've sent a few pics. I sent a friend a pic and it said "no data plan subscribed" I turned off my cellular data and it wouldn't send pics. I need help. I don't wanna run up my bill!

Hey teens! How do you use iPhone apps?

Are they resourceful or more for fun?

I'm creating an app for my college thesis project, and I'd like to know how you approach them.

Are they helpful to you?

How to change the country on your iphone on app store?

My mum's partner shares the same apple ID as me. They went to New York and received a voucher, therefore their app store country changed from UK to USA. They spent most of their voucher but have $0.49 left and their isn't any apps costing $0.49.It won't let me download anything unless i change my country on it and i can't. Any suggestions?

My iPhone 4S is stuck at 1 percent battery?

My iPhone 4S is stuck at 1 percent battery and I don't know what to do I plugged it up to charge and it shoes a battery with a little bit of red and it has been like this for a week now please help and thank you in advance

How much does it cost for 4 lines on T mobile?

One more thing can you buy an iPhone 4s and use T mobile network

Added (1). I mean unlocked iPhone. Can you use the family plan for 4 unlocked iPhone.

Added (2). Can you use the family plan from t mobile for your own phone not from t mobile an unlocked one.