From the wiki:
There are also special numbers which will never be allocated:
-Numbers with all zeros in any digit group (000-xx-####, ###-00-####, ###-xx-0000).
-Numbers of the form 666-xx-####, probably due to the potential controversy (see Number of the Beast).
-Numbers from 987-65-4320 to 987-65-4329 are reserved for use in advertisements.
