Where can I buy a SIM card for straight talk?

I just bought an AT&T iPhone 4 and want to use it for straight talk. The straight talk website says it is compatible all I need is a straight talk SIM card. I can buy it online but I was wondering if I can also get it from Walmart Wireless? The only reason I'm asking is because I don't want to wait for it to come in the mail.

Go to there website they should have a section on there. Or call customer service. I don't know the number though.

Yes, you can purchase a Straight Talk SIM card at Walmart. However, I'm curious how recently you purchased your phone? I ask this because Straight Talk is only compatible with iPhone's that are either purchased through them or are "unlocked", meaning they are out of a contract and have been freed to go to another network.

i have a straight talk phone that has been turned off for a year… I was told my sims card has deactivated… And i needed a new one… So i went to Walmart to get a sims card and they told me it had to be ordered… That they have the sim card for the a new plan where you are switching from a different plan to Straight Talk… This makes no sense to me…