Twelve-year-old Emily McQueen needed to know if you go left or right on the number line to answer a math problem, and she couldn't figure it out herself.

So she called her friends Jasmine Hudson and Christina Wynn. Jasmine then called her friend Terryn Stokely, and Christina called her friend Darrius Heyward-Bey. They all tried to answer McQueen's questions--together, during one telephone call.

It's the newest trend in teenage communication--group phone calls. Youngsters from Los Angeles to Washington are communicating regularly with their friends using three-way telephone conference call features to link as many as 10 people in one telephone call. They talk about everything from tomorrow's homework to who's dating whom to what movie to see on Saturday night.

"It's more fun to talk to a group," said Emily, a seventh-grader at White Oak Middle School in Silver Spring. "If you talk to several friends at one time, everybody gets the same news at the same time. It also saves time because I don't get that much time on the telephone, but I like to talk to a lot of friends. This way, I can talk to everybody at once."

The telephone calls tend to focus on typical adolescent concerns: boys, clothes, friends, parents, schoolwork, activities, music, movies and funny events.

Telecommunications industry watchers said group calling among teenagers started in recent years in some of the bigger cities when youngsters began using "vertical calling features" such as three-way calling, call forwarding and call waiting to reach out and touch their friends.

"It's their party line," said Jeff Kagan, an Atlanta-based telecommunications industry analyst whose 14-year-old son, Jason, regularly talks on the phone in groups.

Analysts said many adults order the extra phone services, then forget about them. But today's youths--who have grown up with pagers, cell phones, fax machines, electronic games, home computers and other gadgetry--are more high-tech than their parents. They are savvy enough to figure out how to use the additional features to make the most of their telephone time.

Three-way calling takes place when one caller dials up two others in a conference call; the two who were called can then each call others, and the connections often grow from there. The service typically costs between $3 and $4 a month, depending on the jurisdiction. In the Washington area, Bell Atlantic charges $3.50 to $4 a month.

Bell Atlantic is contemplating a different pricing system, "looking to develop it on a per-use basis," said Michel Daley, a spokesman for Bell Atlantic. "But I will say it is one of the more popular services. . . . We do know teens are using it, but we have no hard, concrete studies. Just from informal research, we know that teens and adults use three-way for conference calling. We know teens tend to daisy-chain the service."

Some telecommunications systems allow the calls to be made on a call-by-call basis, at a cost of about 75 cents per call.

David Onak, spokesman for Ameritech Corp., a Chicago-based telecommunications company, said the number of phone lines with "vertical calling features" has increased by 18 percent nationally in the last 12 months.

Irma Zandl, president of the Zandl Group, a New York-based trend research firm, said she was in Detroit recently on business when she heard radio ads that marketed three-way calling to young people.

Zandl said that like most teenage trends, party calling started in urban centers such as New York and Detroit among black youths. It has spread to teenagers of all races in the suburbs.

Courtney Bledsoe, an eighth-grader in Detroit, links up with her 15-year-old boyfriend and her best girlfriend by phone from 9 p.m. to 3 or 4 a.m. most weeknights.

"Boys aren't as interested in the telephone as girls are," said Bledsoe, who is 13. "They just kind of listen."

Several group callers said they most often make the calls to do homework. Some admitted selling their parents on getting three-way calling by stressing their need to study with friends. Emily McQueen, of Silver Spring, said she is not allowed to talk on the telephone on weekdays unless she is discussing homework, though others in her group said the weekday conversations are typically at least partly social.

Robin Phillips, 17, a Largo High School senior, turned to "hot line" calling at homecoming a few weeks ago. He was about to fork over $78 for a shirt, but he wanted to make sure no one else planned to wear anything similar. "We all talked about what we were going to wear and where we were going to buy it to make sure nobody had the same shirt," he said. "You do not want to have on the same thing as someone else at Largo's homecoming."

The senior float committee held strategy sessions over the telephone. Phillips's friends plan their weekend outings together. And when one friend bought the new Destiny's Child CD, several of his friends heard it first via a group telephone call.

Jackie Bledsoe, Courtney's mother, said her daughter probably spends too much time on the telephone. But she said her own research shows that "being interested in the telephone is a normal part of their development.

"I hate to take something away from her that she enjoys doing so much," she said.

Vivian Heyward-Bey, Darrius's mother, said as far as she's concerned, that's a good use of the phone.

"They're just friends, and they are talking as friends," she said. "It is positive because they are learning how to deal with each other while they talk."

On a recent blustery Sunday afternoon in Prince George's, a group call was underway. Vogue Wilborn, 12, whiled away the time with fellow Kettering Middle School eighth-graders Kindra Simmons and Aaron Brown, both 13.

There would have been more people on the call, but Victoria Jones was doing something with her parents. The callers also left one boy out of the call because he had upset one of the girls recently.

"I finally went to see 'The Blue Streak,' " a movie, Vogue said. "We didn't get home until after 10."

"I saw it last week," Aaron said. "It was funny."

"I'm itching," said Kindra, who was suffering from chicken pox."

"I feel so sorry for you!" Vogue said. "Lanera's going to have a birthday party."

"Where's it gonna be?" Kindra asked.

On it went, as the conversation lasted more than an hour.

Finally, plans for tomorrow came up.

"I'm gonna sleep 'til noon," Aaron said. He stifled a yawn.

So did an adult who was listening to the conversation.

CAPTION: Robin Phillips, 17, a Largo High School senior, is a regular participant in conference calls with teenage friends.