For Samsung Galaxy S4, model # SAS975G uses ATT, (also Samsung S2 which is outdated and hard to find). It is very important to read this article (link below) before you buy a phone- Straight Talk is not in the business of refunding money for phones. I have a few friends that are stuck with expensive phones that do not work in their area. Easy way of finding out which carrier provides towers for each phone by numbers on the phone packaging box (at Walmart) and check their model numbers, as well as GSM and CDMA. IMPORTANT... check out http/www.prepaidphonenews.com/2011/12/how-to-get-tracfone-net10-or-straight.html