(FORTUNE Magazine) – If there's anything a baby hates, it's the arrival of a newer, cuter baby. For some, that day never comes; but for the Baby Bells (and let's face it, they're not getting any younger) the time is here.

The little Bells now find themselves challenged by a pack of tiny companies that sell Internet access over local phone wires, a service known as a digital subscriber line, or DSL. (Their rise is evidenced by a recent spate of advertising everywhere from Seinfeld reruns to NFL broadcasts.) This technology connects users to the Net through local telephone wires at speeds up to 50 times that of a conventional 56K modem. But DSL providers such as Covad, NorthPoint Communications, and Rhythms NetConnections--all three are publicly held companies--have found, unsurprisingly, that the Baby Bells are resentful about having to make room for them. So for three years the newcomers have been fighting a legal war to get better access.

On Nov. 18 they stand to win their biggest victory yet: The FCC is expected to issue a landmark ruling that will force regional telcos like Bell Atlantic and SBC to let competitors offer high-speed Net access over the same line that carries voice traffic, a process known as line sharing (and one the telcos think trespasses on their sovereignty). At the least, the ruling promises to boost DSL companies' expansion by lowering prices and speeding delivery. Today local carriers require DSL sellers to install an independent line into customers' homes--then the carriers lease out the line for $20 to $30 a month, a cost largely passed on to those customers. As a result, DSL costs around $200 to install and $50 a month. Line sharing should cut consumers' costs by half.

Lawyers involved in the proceedings caution that the FCC could still postpone the decision at the 11th hour. But virtually all agree it's only a matter of time before the commission decides in favor of DSL providers. "The regional telephone companies will lose absolute control over the one existing line into the home," says Mark Langler, a broadband analyst with J.P. Morgan. The early signs certainly point that way: The FCC issued an opinion last spring saying line sharing would "foster consumer choice" in the broadband arena and "promote innovation and competitive deployment" of Internet connections.

The FCC opinion would be only the latest setback in the Baby Bells' fight against DSL interlopers. Ever since the Telecommunications Act of 1996 forced them to open their networks, the carriers have been throwing obstacles in DSL's path, only to see them swept away. For example, Covad, based in Santa Clara, Calif., and the largest DSL outfit in the country, slapped SBC's Pacific Bell unit with an antitrust suit last year, forcing the carrier to open up space in local exchanges for its DSL equipment. (SBC counters that it was already finding space for the gear.) Meanwhile, the phone companies have argued that sharing a line with DSL would affect the quality of voice communication, but in a recent test in Minnesota, US West and Covad demonstrated that it does no such thing. (In fact, Bell Atlantic, SBC, and other carriers have begun offering DSL on their own voice lines.) And the telcos were obliged by FCC rules to disclose that sharing their lines costs them nothing, which means they are prohibited by the Telecom Act from charging DSL sellers a fee.

The Baby Bells, naturally, aren't happy about the anticipated ruling. Tom Tauke, Bell Atlantic's senior VP of government affairs, argues that line sharing isn't mandated by the Telecom Act and that the telcos will probably challenge the FCC's ruling in the courts. But Bell Atlantic will promptly comply with the order, says Tauke, rather than jeopardize its own applications with the FCC to break into long distance. It seems the Baby Bells must accept an unpleasant fact of grown-up life. They're going to have to share.

--Edward Robinson