The deal is designed to give 3Com customers worldwide comprehensive end-to-end local and wide area network access from network interface cards and high-speed modems.
The combined companies, which will have $5 billion in annual revenues, will operate under the 3Com name.
The deal is expected to close this summer and 3Com will take a one-time charge.
Eric Benhamou, 3Com's chairman and chief executive officer, will assume the same office for the combined company. Casey Cowell, U.S. Robotics' chairman and chief executive, will join 3Com's board of directors as vice chairman.