I'm an Android guy and honestly will not use such a phone until Windows Mobile is of the same caliber. However, I am very impressed with this phone and WinMo. The Lumias seem very durable vs. say my flimsy LG G2 (2 screen replacements) or the LG G3.
Note however that these AT&T GoPhones DO WORK on other service providers without unlocking. However they have to be AT&T resellers and you do have to contact and ask them before committing.
Some of these resellers are H2O Wireless, Straight Talk, Red Pocket, AirVoice, Net10. I've compiled resellers by carrier here
AT&T Prepaid Cell Phone Plans and Details - AllPrepaidPlans.com