1- SIM Unlock Samsung Galaxy from AT&T Network by using IMEI:

http://attunlockcode.com/categories/AT%26T-Samsung-Unlock-Code/

Unlock AT&T Network locked devices including all AT&T Samsung, AT&T ZTE, AT&T LG, AT&T Huawei, AT&T Alcatel and all other AT&T supported mobile phones by using the IMEI, so you can use your AT&T unlocked device with worldwide Networks SIM cards