(FORTUNE Magazine) – Could it be that the fax machine will replace the telephone as the umbilical cord that connects the business traveler with the rest of the world? The machines have already infiltrated offices across the U.S. This year, over 860,000 will be sold, more than twice the number for 1987. Now entrepreneurial companies, with an observant eye on the needs of business people, are putting faxes that take credit cards in airport lounges, hotel lobbies, and convention centers. Small companies like Faxplus, Compugram, and Faxit have taken the early lead. Their machines are easy to use. Customers insert a major credit card and dial the fax number they want to reach. Like the ones in the office, the machines can make international connections. They also can receive information. Pay faxes are faster and sometimes cheaper than overnight delivery services. Faxplus, for example, charges $8 for ten minutes, plus the long-distance telephone fee. About 600 machines have been installed so far. Northwest Airlines put 13 of them at U.S. airports, including Boston's Logan and Chicago's O'Hare, and one at London's Gatwick. By the end of the year, United Air Lines plans to install 12 units in its Red Carpet Club lounges around the country. Bill McCue, who publishes a directory of public fax stations, estimates that by the end of 1991, fax freaks will find about 2,000 charge-it machines in the U.S. alone.