GSM and CDMA are different things.
I recently bought a brand new GSM-Unlocked Samsung S8 (International Version) off of Amazon. After it arrived I put my Verizon SIM card from my former phone (a Verizon factory unlocked Galaxy S6) and it recognized my number and showed how many bars I had. However, two days later I tried to send a text but it didn't send. I then tried to make a call and it said that the mobile network was unavailable. Is this easily fixable or is the new phone I bought CDMA incompatible?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic