Captive AudienceFor now, investors have no complaints. They openly marvel at the tech edge that helped transform the teetering Reston, Va., niche player into the most profitable wireless telco in the nation. Specifically, Nextel's push-to-talk feature has helped it run away with a prize portion of the market. Business sales groups, field technicians, medical teams, taxi fleets and security squads have found Nextel's instant radio connections an important communications tool. The phones have become so embedded into government agencies and corporate work groups that price has hardly been a consideration. "They have the ideal captive audience and that lets them charge about 30% more than the rest of their competitors," says Friedman Billings Ramsey analyst Susan Kalla, who rates Nextel a buy. In an interview Thursday, Nextel Finance Chief Paul Saleh turned a question about how much the company was charging into one about how much the company was delivering. "We offer our customers a lot of value and that helps them become more productive," said Saleh.