A number that indicates the FRSW UNI Index that is
is associated with the ISDN Phone Number. This
FRSW UNI Index is used as a key to obtain the UNIs and
the Screening information from the wfFrSwIsdnScrnEntry and
wfFrSwIsdnUniEntry mibs. The default for the index is
2**31 - 1 = 2147483647 = 0x7FFFFFFF, which represents
an unconfigured index number.