CDMA phone for Cellular South

I am possibly changing to Cellular South here in Mississippi and need a few answers. I currently use Cingular(GSM) carrier here and Cellular South is a CDMA carrier, their policy is that if you want to buy a Treo 650 you have to purchase their data plan on top of their voice plan for $39.99. What i am wanting to do is to buy a Treo 650 that works on CDMA(possibly off Ebay) so that i wont have to purchase their Data plan. So basically my question is can i purchase ANY CDMA phone and it will work on Cellular South's system or do the CDMA phones have to be UNLOCKED as well? or can i just purchase any phone off Ebay that works with Verizon(CDMA carrier) and it will work on Cellular Souths system?

Thanks

 

Thanks for your reply, i wasnt sure how the CDMA phones worked, i know that GSM phones can be unlocked and so forth but wasnt sure about CDMA.
Thanks again