My phone isnt recognizing the sim card?

[AC Question]

Im not sure how to program the phone to work as att again. I had recently bought a Samsung galaxy 4 that was an att phone and then they switched it to straight talk and I would like to use my att sim with it and im not sure how

 

[Rukbat]

If it doesn't recognize the SIM card, bring it into AT&T. Either the SIM port is damaged (in which case the phone is going to need repair) or the SIM card is bad, and AT&T will replace it for free. The only change in going from AT&T to Straight Talk with an AT&T SIM is the APN, and you can get that on the web by searching att apn. The SIM card should still be recognized, you just won't have mobile data or MMS until you have the correct APN. Voice and text should work. (The worst thing that will happen if the phone doesn't have to be repaired is that they'll tell you to take the phone to the nearest Device Support Center [they'll tell you where it is] because a bent contact or dirt in the SIM port can be fixed in a minute at the DSC.)