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Bill Nguyen is a serial entrepreneur. He led business or technical development in four startups before founding Onebox.com, a company that was among the first to provide e-mail, voice mail and fax access in a single mailbox over a conventional phone. Nguyen sold Onebox for $850 million in 2000,but not before hearing from wireless subscribers that they lacked similar data retrieval services. His solution? Seven Networks. Software from the Redwood City, CA, company lets customers of a wireless carrier access e-mail, voice mail and other Internet services simply by calling the carrier. Unlike subscribers to other wireless services, Seven customers don’t have to install extra hardware or software. So far, Cingular, Sprint PCS and Britain’s mmO2 have implemented Seven’s innovation, and Nguyen has secured $64 million in venture funding. His company has also partnered with Microsoft to create software that allows a company’s employees to wirelessly tap into its intranet. How does Nguyen do it all? For one thing, he is notorious for sleeping only three hours a day.