Extension type of the line.
extension(1) - Cisco IP Phone line.
intercom(2) - Part of pair of intercom line.
paging(3) - type to receive audio pages.
moh(4) - type to address MoH.
mwi(5) - type to address MWI.
parkslot(6) - type to address call park slot.
loopback(7) - loopback directory number.