Microsoft unit WebTV Networks will raise the monthly fee for its WebTV Plus service to $24.95 from $19.95 effective from June 1, the company said Tuesday. WebTV introduced the new Internet TV service in December, although the needed set-top boxes, which retail for about $200, were in scarce supply until recently. WebTV officials said the increase was partly because users remain online for an average of 41 hours a month.(Reuters) pared with about 24 hours for a user of a computer-based online service. Also on Tuesday, online news service ZDNet reported that competitor NetChannel Inc was closing its main offices.