This is a great question. T-mobile offers truly unlimited nationwide 4g data with no overeages or caps, as well as a blazing fast 4g network. T-Mobile offers some of the best value over the competitiors, and also has really good Monthly 4g plans available if you don't want to sign a contact. t-Mobilealso offers free wifi calling! Using your iPhone on T-Mobile is a great way to keep the device you love while saving money.