How to get iPhone 5 2013 GSM model

So I had AT&T and bought the iPhone 5 from them, on contract, back on December 15 2012. I wanted to save money and have Unlimited Data so I paid an Early Termination Fee to cancel my contract, got my unlock from them, and moved to T-Mobile prepaid $60 plan/mo. So I get Edge coverage, or 3G wherever their reframed 1900 network is. BUT now T-Mobile has their own iPhone that is LTE-enabled, and has the 1700/2100 AWS bands, for 4G/LTE in most places! Can I get my model replaced with this model?? If so, how? It has the same model number as mine but people are referring to it as the "GSM 2013 model".