T-mobile new plan for iphones vs other companies?

So i'm 18 with no credit and i wanted to gett a contract phone. With T-mobile
but i'm not sure if i should go with them. T-mobile has a new jump plans that 50$ a month,
but i have a few question
i get on the internet like crazy & when they say unlimited data does that mean unlimited if not what other companies offer that or what other companies give you more data.
but still keep in mind i don't have any credit so i'm not tryna play a whole lot of fees.( since t-mobile new plan is not an annual contract will i still have to pay fees for me not haven any credit )
& another thing is i want to get an iPhone may 5s or 5c when you use apps on your phone are they running from your data or since its on your phone it dosent matter

I have been a happy T-Mobile customer for over a decade.

First of all, Jump is not a plan for service but the new insurance program. You are not obligated to sign up at all (it is an additional $10 a month for the insurance).

Second of all, T-Mobile no longer requires contracts for new customers (old customers either, once they finish their existing contracts). You will not have to pay any fees. However, they also do not subsidize phones anymore, meaning you have to pay full price for one. This is actually a good thing, you save money but it does cost more up front. They do have payment arrangements on some devices if you qualify.

T-Mobile has the absolute best customer service. It just can't be beat! And I love their plans. We have a family plan and when we changed to one of the new plans earlier this year, we saved a lot of money. The $50 a month includes unlimited talking, texting and data. The data is slowed down after 500 mb. You can conserve your data by using Wi-Fi at home, school, work, or while out shopping. And even after it is slowed down you can still use Facebook, play games, check email, etc. Streaming videos and downloading large apps becomes difficult.