Just because we can do it - just because we own the technology - doesn't necessarily mean we should do it. Just because we own cell phones doesn't mean they are always appropriate. Just because we own computers, doesn't mean e-mail is as formal or as appreciated as a handwritten note.

Technology is changing the way we communicate. But we can still be thoughtful. We can remember our manners as we use our new machines.

Audrey Glassman's new book, "Can I Fax a Thank You Note?" (Berkley Books) tries to find the middle ground between convenience and consideration. She's a moderate. If you read other etiquette experts, you'll find they range from liberal to fascist on the subject of techno-manners.

For example, Peggy Post (Emily's great-granddaughter-in-law) thinks call waiting is fine. She has one caution: Be sure to say, "Mind if I get this other call?" But Miss Manners, Judith Martin, disapproves of call waiting. She says, "Putting previous callers on hold is rude unless your telephone plays tunes to them while they wait, in which case it is unspeakable."

Here's Glassman's take on call waiting: It's vital in offices where there is only one person to answer several lines. But it is still unpleasant for the caller. She says, "If you know there may be Call Waiting interruptions while you're talking to someone, inform him at the outset. You're still being rude, but at least your cards are on the table."

Glassman covers many subjects with the same pragmatism, including technological travails such as these:

- Answering machines. Q: Is it rude to call back when you know the person who called you is not going to answer? A: Not necessarily. Not every call must include chitchat. You can relay information on an answering machine. Let's say you get out of a business meeting late in the day and find a half dozen phone messages. It makes sense to return calls and leave messages, answering your callers' questions, eveni though they've already gone home.

- Speaker phones. Q: Is it impolite to use one without first asking permission of the person you are talking to? A: Yes. Most people don't like speaker phones. The implication is that you are terribly busy and more important than the person to whom you are speaking.

- Cell phones. Cell phones offer endless opportunities to resist the temptation to act like a big-shot.

Q: What do you do if you are with a friend at dinner and he takes out his cell phone to check with the baby sitter or retrieve some phone mail? A: You could express your outrage, but he wouldn't get it. The only thing to do is never dine with him again.

Glassman says, "While there may be slightly greater leeway in business than in social situations, it is always inconsiderate to have your cellular phone on and ringing when you are in the company of other people.

"If you absolutely must keep your cell phone on during a meeting, you should apologize in advance for the inconvenience. People have every right to roll their eyes at you; the people with whom you are meeting deserve your undivided attention.

"It always bears re-examination: Are you doing this because you have to or because you can?"

- Beepers. Keep them on vibrating mode. Never allow them to beep.

- Faxes. Q: Are there times when a fax is inappropriate? A: Yes. If you are applying for a job and the personnel director has said to mail, not fax, a resume.

Also, if you are sending a document of more than a dozen pages. Overnight mail might be more considerate for those waiting in line for the fax machine.

Also, never fax your resignation. And never fire someone by fax. There are times when face-to-face encounters are necessary, albeit unpleasant.

When you want to make a good impression, say for instance when you are submitting a proposal or bid, you might want to send it by overnight mail. What if the person you are faxing gets 11 mailed proposals, typed on lovely rich stationery, and yours arrives on shiny, curly fax paper?

Incidentally, the answer to the title "Can I Fax a Thank You Note?" is this: There are three occasions when handwritten, mailed notes are expected. When saying thank you. When expressing sympathy. When issuing a formal invitation.

In business situations, if you are in the habit of exchanging faxes and e-mail, it is not necessarily rude to include a thanks for yesterday's lunch along with the fax.

But to fax your sister a thank you note for a birthday present she sent you? Etiquette experts agree this shows a cavalier attitude. It's better than not thanking her at all, of course. Still. Try to find a stamp.