The official Tmo iPhone wont go on sale until the 12th with pre-orders on the 5th. That model will work on all Tmo bands from 3G to LTE. This coming update on the 5th will add support to current iPhones, giving proper MMS and LTE connections. If you have an iPhone 5 currently on Tmo, you still cannot get on their 3G if your area has not been refarmed, you still would have to buy the new one.
Thank you!