ST doesn't have an automated retail kiosk (shop) at LAX but according to this list, there are a # of locations in the greater LA area, in addition to Walmart.
T-Mobile has similar prepaid plans at competitive prices, easy to setup & use and given your device, will give you very good 3G/HSPA+ coverage. Look for a T-Mo corporate store and/or authorized agent around town (in shopping malls) - under BYOD (bring your own device) on their prepaid website.
http://www.straighttalkblog.com/2013...ail-shops.html
If you find & select Straight Talk, you can choose a Sim for AT&T's network or one for T-Mobile's network.