While U.S. Cellular phones are CDMA ones, Straight Talk has CDMA in some areas and GSM in others. Depending on what network they are borrowing in that particular area.
You would need to contact Straight Talk to see if that area for them is CDMA or GSM. Only they can tell you for sure.
Also, they aren't interchangeable and you can't change a device from CDMA to GSM or the other way around.