The company will pay about $340m (£236m) in stock and cash for HO Systems and expects to complete the deal by the end of the first quarter of 2002.
VeriSign, which provides secure online trust services, will merge the HO Systems business with its Illuminet Holdings subsidiary.
Cheryl Regan, a spokeswoman for VeriSign, said that HO Systems will add billing and customer care services to the existing Illuminet business, which provides signalling, intelligent network and clearing services for telecoms customers.
HO Systems core product is speedSUITE, an end-to-end billing and customer relationship management package that can help wireless carriers better serve their customers.
"This continues the strategy that Illuminet had," Regan continued. "Illuminet's strengths are in telecoms, and their customers are 900 of the largest carriers in the world."
Because HO Systems and Illuminet provide different services, no redundancies are expected because of the acquisition, Regan said. "They are very complementary services," she said. "They don't overlap."
Illuminet operates the largest independent Signalling System 7 network in North America, providing signalling, intelligent network and clearing services to more than 900 carrier customers in 23 countries.
"As demand for wireless communications grows, so does the need for services that combine the wireless voice and data and billing functions," said Terry Kremian, executive vice president and general manager of Illuminet. "The combination of Illuminet's services and trusted expertise with HO Systems' wireless billing and real-time provisioning systems creates a powerful offering for wireless carriers."