it's all about the towers. For T-Mobile USA you need a phone which supports BOTH 1700 & 2100. The MI-One doesn't support both. I'm going to give a t-Mobile prepay card a shot for one month. I'm going to guess that I will get 3G from 1700 towers but not be able to see 2100 towers. My reception will most likely be ******. I'll report real-world results from Los Angeles, USA