Motorola used very carefully chosen words in the original Moto X PR statement when the phone was announced. We were told the device would be in AT&T, US Cellular, Verizon, and Sprint stores. It looks like that's happening as planned. The PR also said the device would be available for all carriers, including T-Mobile, direct from Motorola. Now the device has appeared on Motorola.com for $599.99.
The listing says the T-Mobile Moto X is available "exclusively on Motorola.com," so that would seem to confirm T-Mobile won't be carrying the device at all.