And many, if not most, of those 1.7 million numbers appear to be used for one thing: redirecting callers to a phone-sex service.
Dial 1-800-Chicago and instead of reaching a tourism hotline for the Windy City, you will hear a woman offering "one-on-one talk with a nasty girl" for $2.99 per minute. A similar thing happens if you punch in the initial digits of 1-800-Metallica, 1-800-Cadillac, 1-800-Minolta, 1-800-Cameras, 1-800-Worship or 1-800-Whirlpool.
All those numbers contain messages redirecting callers to erotic chat lines operated by National A-1 Advertising, a company that shares an office building with PrimeTel, has common ownership and lists many of the same people as executives or business contacts.
Many people who mistakenly dial a phone-sex line probably just get red-faced and hang up as quickly as possible. Others apparently respond to the come-on and hand over their credit-card number.
Founded in 1995, PrimeTel is one of about 400 companies registered as toll-free service providers for the U.S. and Canada.
There is nothing illegal about using toll-free phone services to promote adult entertainment, and callers aren't charged unless they supply their credit card information.
Over the years, though, PrimeTel has been hit with lawsuits and complaints alleging that it is violating federal rules banning toll-free service providers from hoarding digits.
The FCC has never taken formal action against PrimeTel or National A-1, though federal agents and Philadelphia police spent two days in October removing records from National A-1's office suite. But it's not clear if the action was related to the phone business.
The man listed on many government records as the top executive at both PrimeTel and National A-1, Richard Cohen, declined interview requests.
A lawyer for both companies, Charles Helein said PrimeTel isn't breaking any rules or engaging in prohibited practices such as selling numbers or obtaining ones it doesn't intend to use.
"They are extremely sensitive to the FCC . . . They wouldn't have them if they didn't need them," Helein said of PrimeTel's huge pool of numbers.
Helein said the raid last fall was not aimed at PrimeTel. National A-1 and its owners have a variety of business enterprises headquartered at the same address, including a website sometimes used by prostitutes to advertise.
According to a database maintained by an industry organization, PrimeTel was listed as the administrator of record for at least 1,667,000 out of about 7.87 million active 800 numbers as of this March. Industry experts said PrimeTel also holds a dominant share of numbers with other toll-free codes, like 888 and 866, giving it several million numbers overall.
Such numbers are so highly sought-after that several companies have built powerful computer systems that search the database every day, looking for digits of potential value. Numbers can be reserved as quickly as 95 milliseconds after they are released by former users.
Helein said PrimeTel has been the target of complaints from other industry players who are "jealous" of the company's computer systems.