What is at and t or sprint? And how they work?

Like. On the apple website the price of iphone 4s is $99 and if I buy it from at and t what agrement I need to sign up or how much I need to spent… In. Detail please… 10ptss!

At&t and sprint are phone companies. You'd most likely have to get a two year contract with either one if you want a phone from them (unless it's prepaid.) Usually the two year agreement doesn't cost anything, but you have to stay with them and keep up with your bills for 2 years. If you want to break the contract before the two years are up, there will be a cancelation fee (about $300 or less, depending on how long you've kept the phone). If you go on at&t's website, or go to a at&t store (or one that sells their phones), you can learn more about it. Hope this helps.