I am really wanting to get an iPhone 5 16 gigabyte, but I have a galaxy s 4 16 gigabyte. Can I go into T Mobile and tell them I want to trade in? Do I have to have a receipt? Is this even possible? I also was thinking about getting one on Craigslist and purchasing a nano SIM card. How much would that be? I don't really know what I'm doing, & I couldn't call T Mobile so I really need help.