Like buzzing cicadas, wireless investors are getting louder as the summer progresses.The growing chorus of enthusiasm turned up a few notches last week, thanks to a strong sales update from sector darling Nextel ( NXTL). The king of the wireless business communications niche said Thursday that 2003 revenue could top the $9.9 billion currently projected as its unique walkie-talkie features continue to attract and keep customers. But Nextel isn't the only wireless shop entertaining newfound consumer demand despite a tepid economy and rabid competition. It seems a crop of snazzy new phones, heavy promotions and lavish retention offers from telcos are bringing people into stores and keeping would-be defectors from bolting. Encouraged by the level of sales activity usually reserved for the holiday season, some analysts and investors expect second-quarter earnings reports to show gangbuster sales results.