If you want to replace your iPhone 4 for a non name brand try this company as they have some phones that are 3G with 1900MHz in the WCDMA group. You can find this company at www.alibaba.com membership is free to join alibaba and this company will accept a Paypal payment on a sample (1 Unit), or they accept escrow (alibaba holds your money till you receive your purchase and are satisfied), and only use these or credit cards when buying online. The company is Shenzhen Cking Technology Co., Ltd. Try: Shenzhen Cking Technology Co., Ltd. - power bank,tablet pc . You can always go to www.alibaba.com and type in the company name under "suppliers." I'm getting ready to sell my 1:1 Note 2's and replace them with their 1:1 Note 3 ($189+29 s/h=$218). Just a little FYI for you to think about since the phone your thinking about will only give you 2G at T-Mobile, Metro PCS, Verizon, AT&T, and Sprint.
By the way T-Mobile also transmits on 1700MHz and receives on 2100MHz and you must have both these frequencies to get 3G & 4G otherwise it automatically bumps you down to 2G EDGE like it does on my phone. I sell phones and have been trying to get around this and the above mentioned company seems to offer what you need to get 3G. For 4G you need genuine name brands but always check their frequencies first.