They are CDMA, a roaming partner of Sprint and Verizon.
Pretty decent service up here, although Maine is one of their heavily invested markets. Seems like there is US Cellular stores everywhere. Not to mention ads and signs. Looking at their coverage maps for LTE, they have Maine fairly well covered which is impressive.
I helped my girlfriend get their service and there phone selection was really lacking for power users, but she really didnt need much. Their plans have you roam on Verizon EVDO outside of their native coverage areas across the country. International roaming sucks. Overall not bad.