Apple Computer Inc is plunging head first into the market for Integrated Services Digital Networking speech-and-data terminals by way of a joint development pact between its largest foreign subsidiary, Apple France, and the Matra Communication division of Matra SA. The agreement calls for development of a telephone terminal based on the Apple Macintosh, and for complete integration of the AppleTalk local area network with Matra’s PABXs. Direct links to public ISDN networks are also planned.