A Los Angeles start-up plans to unveil a wireless Internet service today that it said will deliver data up to 500 times faster than standard computer modems. InterWireless will launch its so-called broadband service throughout the San Fernando and Santa Clarita valleys and in parts of Los Angeles, including downtown and the Westside, President Richard Elliot said. InterWireless plans to use antennas and ethernet radios to transmit data to customers' computers at top speeds of 15 megabits per second. Internet data are traditionally delivered over phone lines, although some companies are using cable lines, satellite links and other wireless connections. InterWireless will first target businesses, charging them monthly fees ranging from $300 to $900, and will later offer its service to consumers for about $45 a month, Elliot said. InterWireless was founded in October with $250,000 by a group from Canoga Park-based PacificNet, a 3-year-old Internet service provider that has 15,000 customers.