The telephone is, at once, life's greatest aggravation and its greatest convenience. We can't live with it or without it.

It is an annoynance when it rings too much, disconcerting when it rings too little.It is our vital link to an outside - and shrinking - world, but sometimes an intrusion into our own.

It is intrusive when it rings incessantly, at home or the office. At work, a stack of telephone messages - the starting point of a fruitless game of telephone tag - is enough to make one wish the thing had never been invented. At home, when it rings successively for the teenager who isn't home, one is sorely tempted to pull the plug.

Perhaps the phone is at its most aggravating in the hands of sales people and poll takers who work only during the dinner hour. This is not the telephone's fault, but it does prove that advanced technology can be dangerous when it falls into the wrong hands.

Not long ago, just as I was stirring up dinner at the stove, I answered the ring of a survey-taker wanting "just a few minutes of my time." The "few minutes" stretched to nearly 20 while I nervously watched a boiling pot, answered repetitious questions and grew increasingly anxious. I finally broke into the young man's monotonous spiel with a polite protest that I had already answered that. His reply was unnecessarily rude, considering he was asking for favors, and I reacted by hanging up as politely as possible. These are not the manners my mother taught me, but these were trying times. I resolved that if I ever figured out which financial institution the young man was representing, I would be quite certain never to do business there.

I did manage to salvage dinner.

Shortly after that, the ultimate telephone annoyance occurred. It was late evening, the hour when every working person is trying to put a long day behind. I answered the ring to be greeted by a computer voice: "Our operators are busy right now. Please hold the line . . . " I didn't. I hung up, hoping I had inflicted an incurable computer virus.

All of us who live by the telephone express the desire for an occasional reprieve. Our dream get-away is someplace where there are no telephones.

We mean it only half-heartedly, because we're sure to carry our long-distance calling card along with us wherever we go. Perhaps the difference is in being in control. Calling out from a pay-phone down the way is a way of taking charge.

Being able to reach out and touch someone, however, is increasingly important in our personal lives. It is the telephone, and not a letter, that provides a link to distant loved ones.

More importantly, for working parents, it is a vital link to not-so-distant ones. A periodic phone call throughout the working day is a settling and reassuring exercise for parents and children. Taking advantage of it establishes, I'm convinced, a lifetime habit.

When our older son went away to college this year, we were anxious parents wondering how the new alliance would be forged. There he was, stretching his wings and feeling very full of himself. Was he growing up - and growing away, too?

Not to worry.

The phone rings frequently, reaching out to touch us. At odd hours sometimes, because college freshmen have no sense of time. Their sense of space, however, is that home is just a few digits away.

Sometimes he telephones only to say there's nothing to say; other times he can't say enough. Whichever, at the rate he's calling, the semester's phone bills may equal the semester's tuition. We aren't complaining. We're hearing more from him than ever, and he really isn't homesick. Just touching base. It's what he's used to.

The telephone really is a working parent's umbillical cord to small and growing children, a vital link that reassures and solidifies. It's nice to know that it works both ways and that perhaps it can last a lifetime.