3Com Corp. said it will reorganize after its planned $6.6-billion takeover of modem maker U.S. Robotics Corp., which is expected to be completed this summer. The Santa Clara company also announced that its president, Bob Finocchio, will leave on May 31 for personal reasons. The maker of computer networking equipment plans to create three business units to correspond to its major markets. The enterprise systems unit will produce products for large corporations. The carrier systems unit will produce and market products to telephone companies, Internet service providers and other network-service providers. The client access unit's products will be marketed to distributors. 3Com shares fell 50 cents to close at $31.50 on Nasdaq. U.S. Robotics shares rose 25 cents to close at $53.75, also on Nasdaq.