AT&T iPhone 5c 16gb plan

Okay so I'm planning on getting iPhone 5c 16gb on AT&T and I want to do a 2 year contract. After you pay the $100 what do I have to pay monthly for the 2 years?

You sign a contract that you promise to pay whatever monthly plan you get for 2 whole years. Chech their website for all the plans available.

That all depends on a lot of factors including: how much data you added to your plan when Wi-Fi isn't available, accessories you choose to purchase, and service you choose to add to your bill such as insurance, extra warranties and possibly Bluetooth accessories. For the minimum amount of data required to run the service, you will only be spending $60/month. If you go all the way up to 50GB of data, you'll be spending over $400 just for YOUR bill. (Personally 50GB is way too much to add to your plan. How often do you actually use the LTE outside of your home or other Wi-Fi connections?) Just keep that in mind. It's basically the same price as having a singles Verizon account. If you still want the 5C and want to go with a cheaper plan, I do recommend T-Mobile. Sprint's service is terrible plain and simple. T-Mobile is off and on as far as that goes but their plans are freakin' cheap and there are NO data caps. Unlimited literally means unlimited. No overage fees, nothing.