So I got an unlocked T-Mobile S4, data doesn't work for AT&T

[pikachews]

Hi i'm new here.

Today I just traded my unlocked HTC One for this guy's T-mobile but supposedly unlocked S4. Calls work, but data doesn't. In network mode, only GSM/WCDMA works, when I choose LTE/GSM/WCDMA it just gives me no signal and reverts back to the GSM/WCDMA mode back. Help?

 

[Nevets68]

How to Enable T-Mobile HSPA+ AWS Bands on AT&T Galaxy S4 SGH-i337/SGH-i337M! | GalaxyS4Root.com

 

[pikachews]

That wasn't helpful but thanks. After googling for an hour or 2, all I had to do was input "phone" in the APN name. So dumb of me.......