I am currently on Virgin mobile $25 a month plan ( I'm grandfathered in) and I am using the LG optimus V. I've had the phone for about 5 years and it has been a great phone but it is showing its age so I figure its time for a new phone. After looking at all the new phones from Virgin Mobile I wasn't impressed and figure maybe it's time to switch prepaids. I decided I want to go with Straight talk since they brought back the At&t sim cards for them and where I live At&t is extremely decent. Then I also decided that I want the Samsung Galaxy s4 since I keep my phones for a long time I figure I might as well buy the best now and over time it will become average. My only problem is, is I'm not sure which model of the Galaxy s4 to buy. Can I buy a locked one directly from At&t and just put the sim chip in there and will everything work? Or do I have to buy an unlocked international one and use that instead? I've tried looking for myself but I keep getting different answers and I don't want to spend that kind of money if it's not going to work. Any advice or insight would be helpful. Thanks in advance.