Structured T1 means channelised T1 meaning you can define individual channels based on timeslots.
For eg a hub site running FR may have 15 different channels with each channel representing a FR PVC to 15 remote sites
Unstructured T1 means one fat pipe of 1.5 Mbps which cannot be split into smaller channelised links
The VWIC2-MFT would support both
HTH
Narayan