United Online Inc. will expand its broadband Internet service through the network of Covad Communications Group Inc., the company announced Thursday. The expansion of the NetZero DSL broadband Internet service will take place toward the end of the first quarter of 2007. Woodland Hills-based United Online launched its NetZero DSL service in November to provide its customers with an opportunity to upgrade to broadband from dial-up. San Jose-based Covad operates the nation’s largest facilities-based network. “Through this agreement, United Online has the opportunity to benefit form access to Covad’s network and their expertise in broadband,” company Chairman and CEO Mark R. Goldston said. “We believe it will enable us to expand our NetZero DSL broadband offering and give more of our NetZero customers who want a broadband experience the ability to easily upgrade from dial-up while keeping their NetZero e-mail address.” With the addition of the Covad network, NetZero offers broadband service to 30 percent to 35 percent of United Online’s current ISP customers.