Today at GigaOM's Mobilize conference in San Francisco, T-Mobile's chief technology officer, Neville Ray announced that 3G data is now live on the iPhone friendly 1900 MHz band in Las Vegas. Ray said that T-Mobile plans to roll out 3G on 1900 in many more markets by the end of 2013. He didn't say which markets but other sources have mentioned San Francisco, Seattle, New York and Washington. There's a crowd sourced map of places where iPhone users have spotted T-Mobile 1900 3G. The new 1900 Mhz 3G service will be available to both postpaid and prepaid subscribers.
Users with current T-Mobile phones that only support 1700 Mhz 3G will not be effected by the refarming. 3G on 1700 Mhz is not going away, at least not in the next few years.
Moving on the T-Mobile's LTE roll out, Ray confirmed that LTE deployment will start early next year and will be nationwide by year end 2013. No word on if and when T-Mobile will allow prepaid customers to use LTE.