Among the more mystifying rites practiced by teenagers everywhere is the nonstop, often acrobatic telephonic chatfest. We will be the first to admit that these talkathons can be beguiling as well -- especially if the dispenser of gifted gab is as well-connected as our lovely April Playmate, Roberta Lane. Bobby-soxed Bobbie delights in dialing her confidantes for an exchange of girl-talk about the hopeful male operators who feel, as we, that her pert face, live-wire personality and captivating party lines (34-21-34) are worthy of close attention. Nineteen-year-old Miss April, a nifty queen from Queens, New York, harbors sweet dreams of an acting career in TV; while waiting for the big break she helps to pay her phone bills (last month's local calls: $26.18) with secretarial work in New York City. Accustomed as she is to private speaking, this belle telephoner also takes an active interest in such outdoor pursuits as horseback riding and long walks in the country, and waxes enthusiastic over Scottish bagpipe music, dancing (she's a whiz at modern terpsichore, both interpretive and popular) and attending Broadway shows -- à deux. While she currently is not overly concerned with matrimony, our 5'2" communications expert vows that the guy who eventually gives her a ring will be a warm, fun-loving type who steers clear of white lies and blue language. In the accompanying foldout, Bobbie radiates her own fun-loving warmth as she sits all alone by the telephone, a person-to-person smile on her sunny face, an inviting call in her bright blue eyes. In view of which, we invite you to join us in a ready response to Miss April, our entrancing talk of the town.