No. It is neither GSM network nor with unlocked SIM card. It has no slot for a SIM card. It is locked to Cricket CDMA network.
The Cricket Samsung Galaxy Discover Smartphone is a CDMA phone I was told by Straight Talk when I called them. Sometimes the decription of the phone will state which one it is (GSM or CDMA), or maybe it will be on the instruction manual that came with your phone. If all else fails, you could call Straight Talk directly using their 800 number and they will be able to tell you like they did for me.
Also, I found this info on a Consumers Reports webpage when I was researching cell phones:
"Before you buy a phone, consider the service provider. Major carriers rely heavily on two incompatible digital networks. Sprint and Verizon networks use mainly Code Division Multiple Access (CDMA) technology, while AT&T and T-Mobile use Global System for Mobile communication (GSM) technology. All of those carriers also support high-speed data networks. The network plays a big part in the capabilities your phone will have and, to some extent, its performance. Learn more about the service providers in our Ratings (available to subscribers)".
From what I understand, the term "unlocked" means that it is a phone that can use any carrier because it's not "locked" into one specific cell phone carrier. But I think there may be a fee charged for unlocking the phone as I read someone's comment somewhere regarding this.
Hope this helps.