Surely your son would not have abandoned his premedical studies and embarked for Morocco without letting you know first. There must be some other reason why he hasn't returned your phone calls for three weeks. But a person does wonder. The next step might be to send him a Call Me Card. Inside he will find a Bell System gift certificate which will permit him to talk to you free for 24 minutes. That ought to be enough time to listen to his excuses. Call Me Cards can be used anywhere in the continental United States, from Saturday at 8 a.m. until Sunday at 5 p.m., or Sunday through Friday after 11 p.m. Card designs include Celebration (confetti and streamers), Bouquet (pastel and floral), Chrome (brown and macho) and Love Parcel (tan and messily-wrapped). They can be sent directly to the recipient. When he gets his phone bill, he sends in the certificate as payment. If your conversation lasts for 26 minutes, he pays the difference. You will probably find that he has been spending night and day in the zoology laboratory. Apologize for your suspicions and wish him good luck.

Call Me Cards. $6.95 each plus $1.50 handling and shipping for the first card, 50 cents for each additional one. Call Me Cards, Department RA, 812 Fifth Ave. N., Seattle, Washington 98109. 800/228-5505.