4G LTE...but throttled to near 3G for most newer accounts. There are a few older grandfathered accounts that are still active with 4G...but nothing new.
There is a $30 4G LTE data only plan available though.
All phone calls must go through he 3g HSPA-type network and can also be used for text messaging and data. The LTE network cannot be use for voice services, but can be used for text messaging and data.