PCS is a part of CDMA, Sprint exclusively uses PCS on their home digital network, while Verizon uses PCS/CDMA on theirs. Currently your Sprint phone will be able to roam off of other CDMA/PCS networks, and depending on the plan you won't pay for it.
GSM is totally different, and unsupported by your phone. It's used by Cingular/T-Mobile/ATT, nothing you need to worry about.
As far as SAR goes, ignore it. They're all tested and approved before hitting the market, you won't get cancer from cellphone usage.