Explain the difficulty from switching to MetroPCS to AT&T?

I'm 15 years (kinda) and my phone is from MetroPCS. I don't like Metro. I didn't choose it, my mom did. I don't like it because it's so horrible. Their coverage isn't really that great and their 4G is so slow. I have friends with phones from other carriers such as the ones on my question, and their phones are decent-fast speed, but definitely faster than mine. I asked my mom if we could switch to at least AT&T, but she said no. I asked her why, and she something along the lines of too much money and contracts. I don't know. But isn't the same thing? I don't know, maybe since I'm a teen I don't really know that much about phone plans or whatever. So can someone explain it to me please? Can you try to tell me why my mom doesn't want us changing from MetroPCS to AT&T? And could you give me ideas on how to convince her to switching please? Thank you

I was kinda eyeing this phone from AT&T and it's only $0.99 dollars WITH A TWO YEAR CONTRACT. Explain that to me please.

<>>http://www.att.com/shop/wireless/devices/apple/iphone/4-8gb-black.html#fbid=Nz_ohr4y7-1>

Don't even eye the iPhone 4.In 2013, I'd classify it as a piece of garbage. I have AT&T and I can tell you, it is not very cheap. Of course, I work with my dad so I'm able to pay it. I'll tell you my plan if that helps. I have a two year contract and since I got a new contract, I got the Galaxy S4 for $200. If I hadn't gotten the contract, the phone itself would be like $629, 99. My plan is 300 minutes, unlimited texting, and I believe like 4GB of data plan for about $90 a month. Oh, and a two year contract means you have to pay for your plan for 2 whole years and if you want to cut the contract, you have to pay an early termination fee of about $250. Unless you're willing to pay more, just stick with Metro Piece of S**t. Hope I helped.