What are the disadvantages using an iPhone on T-mobile network?
You can use unlock iPhones on T-Mobile network. There is no hidden charge but there is no point of using an iPhone if you cannot get on 3G. The network connection is going to be extremely slow. If you only use the phone for placing and receiving calls, I guess you don’t care. However, you really don’t want to bring an iPhone and use none of its special features.