The Federal Communications Commission allowed telecommunication companies to compete with the incumbent local exchange carriers for services, usually by forcing the existing sole service provider to lease infrastructure to other local providers. Because of the original design of the numbering plan and the telephone switching network that assumed only a single provider, number allocations had to be made in 10,000-number blocks even when much fewer numbers were required for each new vendor. Due to the proliferation of service providers in some numbering plan areas, many area codes fell into "jeopardy", facing exhaustion of numbering resources. The number blocks of failed service providers often remained unused, as no regulatory mechanism existed to reclaim and reassign these numbers.