s that served them wanted "full house" coverage across major metropolitan areas. That often required numbers in doz- ens of rate centers. So a small rate center that might have had a single ILEC pre- fix code now might have five or six CLEC prefix codes, most of them using only a handful out of their 10,000 numbers. This could have been alleviated in sev- eral ways. ILECs could have consolidated rate centers, giving larger local calling areas. But that would have cost them short-haul toll revenues. States could have allowed CLECs to have "oddball" prefix codes that were local to the entire LATA or metropolitan area, but that would have given them an apparent advan- tage over ILECs. The ILECs actually did make such prefix codes available under their own tariff, but they were charged at switched access rates: The subscriber paid by the minute to receive calls. That was a nonstarter in the ISP market. So the CLECs got the same result by grabbing large numbers of prefix codes. This led to repeated area code exhaust. CLECs Winning Strategies Are Met by Rule Changes The problem was finally solved when local number portability (LNP) became widely available. The Telecom Act required the industry to develop methods of making local telephone numbers portable, SO a subscriber could change carriers and keep its number. This was not, however, all that easily accomplished; competition began before LNP was in place. By the late 1990s, the industry had adopted a standard method for LNP; it then had to be phased in to the network, starting with the largest markets. But even LNP left the CLECs needing "NXX" prefix codes of their own because the ILECs did not willingly issue new numbers from its own pools to CLEC subscribers. The real answer finally turned out to be thousands-block pooling. This made use of the LNP mechanism to divide a prefix code among multiple carriers. Carriers would then be rationed numbers 1,000 at a time, allowing up to 10 carriers to share a single prefix from which each could assign new numbers to its own 