WHEN students in Cynthia Silverman's English class used to walk in without their homework done, either because they had been absent or absent-minded, there wasn't much the teacher could do.No more. She and other teachers at Torrance High School record homework assignments and other messages on a special telephone hot line that students or parents can call in on to check. Excuses are now as tolerated as spitballs. "I don't bend," says Mrs. Silverman. "I say, 'Did you call the hot line?' It allows me to turn responsibility over to the student." In an age of hectic lives, when the only discourse between parents and teachers might be five minutes at an open house, schools across the country are turning to the telephone to forge new links between the home and classroom. Computerized voice-mail systems are being used to give out Johnny's reading assignment, list lunch menus, monitor absenteeism, and allow the principal to inform parents of emergencies such as broken-down buses. "It opens all kinds of lines of communication," says Mary McCullough, assistant principal of the high school here, south of Los Angeles. About the only ones who seem dubious are students who can no longer hoodwink elders. "If you don't want to do homework and have your parents find out, it isn't so good," says Summer Breese, a junior at Torrance, who says she has no such problems. "I think it is a good idea on the whole." Computerized voice mail, used in business for years, has just started to show up in classrooms the past couple years. Systems now operate in more than 200 schools in 23 states. "People say technology in schools and everyone wants to run and look at a computer lab," says Cheryl Williams of the National School Boards Association. But this is "one more step in equipping professionals with the tools they need to get their job done." Although systems vary, most allow parents and students to call in day or night using a touch-tone phone. Callers punch in a code, which connects them to a recorded message from their child's teacher. Most instructors try to give out more than the day's homework assignment. They mention key points discussed in class and suggest topics for conversation between parents and kids. "More kids are bringing in their homework completed," says Bruce Baron, principal of Los Naranjos Elementary School in Irvine, Calif., which installed a system last year. "They are better prepared for class. There are fewer conflicts." Some systems can be programmed to call parents about closings or student absences. Torrance High lets parents know when report cards come out. A few voice-mail systems permit parents to leave messages for teachers. Some have balked at this idea, however. Teachers are leery of coming in to a half hour of messages in the morning, some not cordial. Hot lines pose other tradeoffs as well. Teachers have to record messages regularly, though most say it becomes a simple routine that ends up saving time: They don't have to repeat homework assignments to every Tom, Dick, and Mary who missed them. Hot lines vary in price from $10,000 to $20,000 and entail monthly phone bills. Torrance's, a product of Advanced Voice Technologies of Nashville, cost $14,000. A number of schools have had private foundations or corporations underwrite their systems. Los Naranjos has an enrollment of 500. It is getting about 250 calls a day. Eighteen-hundred-student Torrance, whose system is less than two months old, is getting 400 calls daily. Parent Linda Truchin phones in periodically "just to check and see what my son isn't telling me." "He is a very good student," she says, "but he is quiet. He doesn't tell me everything that is going on." Senior Kristen Baltz calls to clarify homework assignments. "It's wonderful," she says. What about parents looking over your shoulder? She laughs. "When it first came out, my dad called up to check on all my classes and my boyfriend's classes and told us what homework we had."