AT&T; will unveil some office computer equipment.

The equipment to be introduced next Monday is expected to allow AT&T;’s mid-size computers to communicate with IBM’s large, or mainframe, computers. It is another step in the telecommunications firm’s move into the office automation market, which is dominated by IBM. Compatibility with IBM’s mainframe computers is considered essential to success for any non-IBM computers, and other firms have already moved in that direction.