Can Straight Talk Use Unlocked Phones

Does Unlocking Your Phone Damage It here.

I'm on straight talks fancorps team it's where you earn points by doing certain tasks, and the points can be exchanged for rewards like phones, anyway I'm going to be ordering the iphone 5 reward through straight talk and asked of it was CDMA or GSM, cdma phones will get little to no service in my area as there's not a tower close enough, but straight talk said this 'As stated earlier, the iPhone we have in stock is designed to run on a CDMA network. If you would like to run on GSM through Straight Talk, you must first unlock the phone as it is currently locked to run on a specific carrier's network. Unlock Iphone 5c Ee.