The program has been implemented in much of the United States by state regulators. A limited number of cities have also implemented rate center consolidation; fewer rate centers resulted in more efficient use of numbers, as carriers would reserve blocks of 1,000 or 10,000 numbers in each of multiple rate centers in the same area even if they had relatively few clients in the area. (A rate center is a geographical area used by a Local Exchange Carrier (LEC) to determine the boundaries for local calling, billing and assigning phone numbers. Typically a call within a rate center is local, while a call from one rate center to another is a long-distance call.) Together with aggressive reclamation of unused number blocks from telecom providers, number pooling has reduced the need for additional area codes, so that many previously designated area splits and overlays have been postponed indefinitely.