[AC Question]

Hi, I have a Galaxy S4 from Tmobile and I wanted to switch to ST. The phone is unlocked and GSM obviously. But my one concern is that I have one of the older ATT straight talk sim cards and was wondering if I could actually get ATTs service with that. Where I am from I have really crappy T-Mobile service and T-Mobile is probably the WORST customer service I have ever encountered, not to mention them changing my entire service plan for and charging me over $400 a month for four devices on the plan. Sorry ranting but could anyone just shed some light on the Sim card deal. I have no tried to test it yet because I'm Still in a deal with T-Mobile. Thank you again for anyone reading this.