DEAR ABBY: When I was 16 and unmarried, I had a son I'll call Josh. Two and a half years later, I married "Joe," who adopted Josh and has raised him as his own. We now have two more sons.

Josh has always known he was adopted. Last week he asked, "How did I get born if we didn't know Daddy then, because you said it takes a man and a lady to make a baby." (Josh is now 7.) Lucky for me, his little brother had to go potty, so I got out of answering his question, and it hasn't been asked again - yet.Josh knows his real father ("Bud"), but he doesn't know he is his father. They get along well, although Bud sees him only at Christmas and on his birthday when he comes over to give Josh his presents. I wish Bud wouldn't come around at all, but Joe wants the two of them to have a good relationship.

How old should Josh be when we tell him about his real father? And what do I say to Josh the first time he says to Joe, "You can't tell me what to do - you're not my real father!"

My family and friends don't think we should tell Josh until he's 18. What do you think? - KEEPING MUM IN DULUTH

DEAR KEEPING MUM: Since your family and friends know who Josh's father is - and Josh is already digging for the truth - the time to tell him is NOW. And if he comes up with the lines about your husband not being his "real" father, the answer is, "He may not be your birth father, but he is the father who is raising you, and that's about as `real' as a father can be."

DEAR ABBY: I am a self-employed woman and work out of my home. I have a friend who often calls me from her office job to "chat" whenever she has some free time. I then have to stop whatever I'm doing and listen to her long-winded, inane chatter. She often puts me on "hold" so she can "catch the phone" when she gets a call on another line.

I am angry at myself for not speaking up, but I honestly don't know how to avoid getting involved in these conversations with her. Any suggestions will be appreciated. - OFTEN STUCK

DEAR STUCK: I wish all the questions were as easy as this one. When you hear your friend's voice, tell her you are busy and will call her back.

If at any time during the conversation you feel bored, or imposed upon, tell her you have things to do and have to run.

Anyone who is held hostage on the telephone must learn how to say, "Sorry, I can't visit now. I'll call you when I'm free."

Want your phone to ring? Get Abby's booklet, "How to Be Popular" - for people of all ages. To order, send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Popularity Booklet, P.O. Box 447, Mount Morris, IL 61054. (Postage is included.)