WASHINGTON -- Rebecca Ryen hears the ring, ring of the telephone and lunges for the receiver eager to hear a friendly voice at the other end of the line.
But then she pauses and checks her Caller ID box to find out if it will be a friendly voice after all."When 'unavailable' comes across, it's either a phone company or a bill collector," said Ryen of Bethesda, Md. "And that means I don't answer it."
She is among millions of phone users hooked on technology that gives them information before, after and during calls. A study of consumer behavior by Arbitron NewMedia found that Caller ID customers have quadrupled over the past four years.
"It's a never-ending source of amazement how much customers love these things," said Terry Yarbrough, senior director of product management at BellSouth, where more than 40 percent of the company's customers have Caller ID and 35 percent either use or subscribe to Call Return, activated by dialing *69 to trace the last incoming call.
SBC Communications' Southwestern Bell, the main provider of local phone service in Texas, Kansas, Missouri, Oklahoma and Arkansas, boasts an even higher Caller ID rate: More than half of their customers have the feature, with 70 percent subscribing in Laredo, Texas.
Phone companies are responding to demand by developing new features.
The latest example: Bell Atlantic's Call 54, which enables people to find out the name and address that corresponds to a local phone number, as long as both the name and address are listed. To get the information, a person calls 555-5454 and then dials in the phone number. A recorded voice reads the name and address.
This service is a response to the growth of Internet and CD-Rom search services, say company officials. With Call 54, consumers can look up three listings for one 75-cent call.
Since its introduction in 1995 in New Jersey -- followed by rollouts in Maryland, West Virginia and parts of northern Virginia -- more than 10 million addresses have been handed out.
Privacy groups say these phone features can put those who want to safeguard their home numbers and addresses at a disadvantage.
With some features, the burden is on the callers to "opt out" of being identified by blocking their number or calling through an operator, privacy advocates point out.
"These services show how users of all kinds of communications systems need to be aware of what they are unwittingly consenting to," said Jim Dempsey, senior staff counsel at the Center for Democracy and Technology, a Washington-based privacy group.
The cat-and-mouse technology game can get harried: To dodge the Caller ID system, a caller can activate a feature to block the number and have it show up as "Unavailable" or "Anonymous."
Phone users can one-up the clever caller by blocking calls from certain numbers. Ameritech's Privacy Manager, introduced last year, intercepts unknown callers and asks for identification.
Even Call Waiting, the veritable grandfather of phone features, is getting a makeover: A deluxe version lets people use Caller ID in conjunction with Call Waiting. Other phone carriers offer a version for Internet users that flashes the incoming number on the computer screen.
Such advances could redefine what consumers consider phone must-haves. In "deprivation" studies conducted by SBC, customers in focus groups revealed their dependency when their phone services were taken away.
"A lot of people just felt like they had no friends" because they didn't know who had called, said B.J. Mamuzic, senior director of consumer marketing.
Ryen admits she's addicted to her Caller ID. She once pulled the batteries out of her fire alarm to keep the gadget running.