Reason i ask is due to how AT&T forces users with smartphones to get a Data Plan, and the only way for AT&T to find out if your using a smart phone is through the IMEI.
I got a T-Mobile Moto X for my wife who is coming from an iPhone 4S on At&t. We went to the At&t store last night to get her Moto X activated and they had a hard time activating it. They ended up doing some kind of trickery using an IMEI number from an At&t Moto X that they had in the store in order to activate data on her phone. That might mean that At&t does not have the T-Mobile IMEI numbers yet for the Moto X.
Short answer: no. Their system actually recognized my T-mobile Moto X as a generic GSM phone and dropped my data plan when I went to get a new nano SIM for the phone, so in theory... they would technically not force a data plan on you with that phone.