From usenet:

900 Series Prefix to OCN translation table

Please note that this differs from the 800 table, because much
fewer of the 900 NXXs are assigned.

NXX OCN        NXX OCN        NXX OCN        NXX OCN        NXX OCN
200 ATX        202 Ameritech  210 ATX        220 ATX        221 TDX
222 ONC        223 TDX        225 Pac. Bell  226 MCI        233 TDX
234 TEN        240 U.S. West  248 Ameritech  250 ATX        258 TEN
254 TTU        255 SNT        260 ATX        264 ADG        266 CSY
272 Bell Atl.  273 CAN        275 ITT        280 Ameritech  282 LGT
283 Pac. Bell  288 GTE N.west 297 CAN        300 ATX        301 Ameritech
302 Ameritech  303 Pac. Bell  321 TEN        322 TDX        327 ETS
328 ATX        331 TET        332 PLG        333 U.S. West  335 Bell Atl.
342 ATX        344 ATX        345 ALN        346 United Tel.350 ATX
364 GTE N.west 366 ONC        369 TEN        370 ATX        377 GTS
386 United Tel.388 SNT        399 ARZ        400 ATX        407 ATX
410 ATX        420 ATX        422 ALN        426 PLG        428 Ameritech
430 U.S. West  444 ONC        445 PHE        446 MCI        450 Ameritech
451 CAN        456 TEN        463 United Tel.478 AAM        479 ARZ
480 ATX        483 GTE Midwest488 ONC        490 U.S. West  500 ATX
505 Pac. Bell  520 ATX        529 MIT        536 BUR        540 ALN
543 ALN        545 GTE Calif. 550 ALN        555 ATX        567 ALN
580 U.S. West  590 ATX       ÿ595 CAN        600 ATX        620 Ameritech
624 Pac. Bell  626 CSY        628 Ameritech  630 CAN        633 MIT
639 PLG        643 CAN        645 CAN        650 ATX        654 TEN
656 SNT        660 ATX        661 United Tel.663 MDE        665 ALN
666 ONC        670 CAN        677 CAN        678 MCI        680 ATX
686 LTG        690 CAN        698 NY Tel.    699 PLG        701 Bell Atl.
710 TGN        720 ATX        722 Pac. Bell  724 RTC        725 SNT
727 GTE Calif. 730 ATX        739 CSY        740 ATX        741 TEN
746 ITT        750 CAN        753 ALN        765 ALN        773 ATX
777 Pac. Bell  778 Ameritech  780 Ameritech  786 ATX        790 CAN
792 CAN        801 Bell Atl.  820 ATX        830 CAN        843 Pac. Bell
844 Pac. Bell  847 United Tel.850 ATX        860 ATX        866 AAM
870 CAN        872 TEN        887 ETS        888 CIS        900 TDX
901 Bell Atl.  903 ATX        909 ATX        924 Ameritech  932 ATX
948 ARZ        949 MIC        963 TEN        970 MIC        971 MIC
972 MIC        973 MIC        974 ALN        975 ALN        976 ATX
988 MCI        990 MCI        991 ALG        993 SNT        999 TEN