The first deployment of an overlay plan with forced ten-digit dialing for local calls on June 1, 1997, in Maryland's area code 301, also led to consumer confusion as the same point could now have multiple area codes. Public resistance to the introduction of new area codes, whether through overlay plans (which allowed customers to keep their existing numbers, but broke seven-digit local calling) or through split plans (where the area code of existing numbers was changed), prompted the FCC and state telecommunication commissions to introduce and encourage the allocation of number space in smaller blocks of 1,000 numbers, with each block consisting of a prefix and the first digit after the prefix. These developments largely coincided with the deployment of local number portability (LNP), a scheme which allowed subscribers to keep their existing numbers when switching to a different provider in the same community. The original LNP database contract was granted in 1996. The number pooling scheme relies on LNP as it relies on carriers to return blocks of mostly unused numbers. The thousand-number blocks being returned to the pool may be "contaminated" with up to a hundred working numbers which must be ported to a block which the carrier intends to keep. In 1998, the director of the North American Numbering Plan Administration had estimated the NANP would have run out of area codes for 10-digit phone numbers by 2025 at then-current rates of depletion. An initial number pooling trial was conducted in area code 847 in Illinois in April 1998. Nortel had implemented support for thousands-level routing of calls in its equipment by 1999. Pooling trials were conducted in 34 area codes across a dozen US states between 1997–2000. The 847 area code, located northwest of Chicago, had already been subjected to multiple area code splits and a proposed overlay area code 224 with 11-digit local calling was drawing public backlash; inefficient allocation meant that some providers had been holding 10,000 number blocks in rate centers where they had few clients or even no clients. A carrier with a few thousand clients scattered across multiple rate centers often had 50,000 allocated numbers. The state's telecommunications regulator, the Illinois Commerce Commission, at the urging of consumer advocates, pushed back against industry and FCC demands for a distributed overlay on 1-847 from 1999 to 2001 as half of the existing 1-847 numbers were not in use. The Citizens Utility Board, a Chicago-based consumer group, attempted to litigate against an arbitrary FCC requirement that calls within the same area code be dialed with the area code when 224 was introduced in 2002, but to no avail.