Cisco Systems Inc. said it bought a minority stake in Belle Systems, a closely held Danish firm whose software lets phone companies generate detailed bills for sophisticated Internet services. San Jose-based Cisco, the No. 1 maker of equipment that links computers to the Internet, declined to provide details on the size of its investment in Holbaek, Denmark-based Belle. Cisco has been selling the company's software to European telecommunications carriers since January. Internet providers traditionally have offered one version of their service and billed for it using monthly or hourly rates. Using new equipment, they now can offer high-speed Internet access and sophisticated services such as videoconferencing. With Belle's software, telecommunications providers can bill for these premium services at a higher rate than basic services, increasing their Internet profits. Cisco shares rose 63 cents to close at $94.88 on Nasdaq.