There is an AT&T store immediately north of the airport at
8949 South Sepulveda Blvd. A T-Mobile store is located a bit farther from the car rental facilities to the south of the airport at
309B N Sepulveda Blvd, El Segundo. There is another T-Mobile store at the Westfield Culver City mall which is a couple miles north of the airport at
6000 Sepulveda Blvd.
Personally, I would not go to Fry's to buy a SIM card, especially, if I just got off a long haul flight; it's just too hectic and their customer service leaves a lot to be desired.