How to access my data on my iPhone?

I have a GoPhone plan from AT&T and i just bought my cousin's iPhone and everything works pretty well but there's two things I don't know. 1. How do I send MMS texts? And 2. Why can't I use the Internet on it unless I'm in Wi-Fi even though I paid for 1GB two days ago?

AT&T does not support the iPhone on their GoPhone plan, they want you to purchase their iPhone data plan instead. So it will work as a phone with the GoPhone plan but internet access won't work correctly unless you buy into their service. (Sorry).

Edit: I didn't realize go phone was an AT&T prepaid plan.b is right, you can't use the AT&T gophone plans. There are third party MVNO plans that uses AT&T such as Straight Talk, Net10, Red Mobile. These plans are much cheaper anyways, for the SAME service. I have the iPhone 5 on net10, which uses AT&T's network. I pay $50/month for unlimited talk, text and 1.5GB of data.

If you activated the SIM for your prepaid service and installed it into your phone (put it inside the tray), it might be that you haven't set up the APN settings for your phone. For any unlocked phone, you have to manually set up the APN. Which is Really EASY.

1. Connect your iPhone to a Wi-Fi network. (You need to connect your iPhone to the Internet to do this).

2. On your iPhone, use safari and go to unlockit.co.nz.

3. Select "create APN" at the bottom panel.

4. Select your network (which is go phone I assume).

5. Click "create apn"

6. Click install at the top right corner.

7. When it's complete, reset your phone and it should work.

Email me if you have any further questions.