ill being near a home for their customers' modems. The Great Telecom Meltdown And when an ISP created a CLEC, its relationship with the ILEC changed. It was no longer a subscriber; it was a peer. The circuits between the two carriers' networks were no longer PRIs, costing several hundred to a couple of thousand dollars per month apiece. They became intermachine trunks (IMTs), circuits interconnecting the two carriers that each carried half of each call. And under the FCC's rules for CLEC interconnection, IMTs were paid for by the carrier that originated the call. For ISP-serving CLECs, that was almost always the ILEC. For a dial-in ISP, sticking with the ILEC became a serious cost disadvantage, compared with their competitors that either teamed with, or became, CLECs. "Virtual NXX" Made Dial-In Available in More Areas The CLEC sector really did show innovation. One important if controversial one happened almost by accident. CLECs were not allowed to put switches in ILEC central offices, SO they installed regional switches that served many exchange areas. This made it possible to offer foreign exchange service across the switch's serving area at no incremental cost. A Santa Monica ISP needing a downtown Los Angeles number from Pacific Bell would get a foreign exchange line, paying for mileage between its site and Bell's switch in the central Los Angeles exchange. (And since Santa Monica was GTE's territory, coordinating the line's installation was that much more difficult.) But a Santa Monica ISP getting numbers from a CLEC could get Santa Monica numbers, Los Angeles numbers, San Fernando Valley numbers, and quite possibly the "full house" of greater Los Angeles' many local calling areas, all on the same lines. This aggrega- tion of foreign exchange numbers on one switch for the purpose of creating additional local calling areas came to be known as virtual NXX [5]. CLEC- serving ISPs adopted it in droves. That, in fact, was a major reason why there were SO many area code splits between 1996 and 2000. ISPs and CLEC