Locked ATT 4s on straight talk?

I seen online that I could use a locked att iphone 4s on straight talk as long as i buy the mico sim card that straight talk no longer sells. I bought it on amazon and i activated it with straight talk but when i put in in my phone it says no service? What do i have to do?

Go to the Straight Talk website and find the APN settings for AT&T phones.

http://www.straighttalk.com/wps/portal/home/support/apn#.UtmaBnmA3IU

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