Caller I. D., the phone-company service that lets you see the number of the person who's calling before you pick up the phone, has touched off a heated debate. Advocates say Caller I. D. guards privacy. Opponents say that callers should have the option of hiding where they're calling from by blocking their numbers from being displayed. Phone companies say blocking would make Caller I. D. less effective in, for example, discouraging obscene or threatening callers.
Now, Northern Telecom Inc. and American Telephone & Telegraph Co. are quietly working on a way to please both sides. Their new scheme allows a person to block calls from phones whose I. D.s are concealed. Stymied callers can then redial and get through--but only by punching in a code that lets their numbers be displayed. The systems may be available this summer from several phone companies that offer both Caller I. D. and blocking, such as Centel Corp.'s unit in Nevada. Another upcoming service, which was to become available on Feb. 18 in Boise, Idaho, translates a displayed number into the name of the person to whom it belongs.