THAT DO-IT-YOURSELF SPIRIT, more than the promise of riches, is what has motivated so many pro and amateur developers to try their hands at iPhone apps. Take the experience of Toby Batton, chief executive officer of Resistor Productions, which develops massively multiplayer online games. Last December, without enough money in the bank to fund production of an ambitious project, Batton and his peers read about the success of iFart -- which, priced at 99 cents a download, reportedly cleared $40,000 for its creator in a single day. “We said to ourselves, ‘This is so, so stupid.’ Then we tried to come up with ideas of our own,” he recalls.

Around a month later, they birthed iGirl, an application in which the user can prompt an animated, three-dimensional female model to dance, talk, and giggle. At its peak, iGirl was being downloaded 12,000 times per day; it was up to 400,000 total downloads at 99 cents a pop by mid-July. “It kind of saved us in terms of getting the money for the video game we wanted to do,” Batton admits.

Pope broke out of the pack with Wait Watchers, which tracks in real time the wait times for rides at Walt Disney World, Disneyland, and Universal Studios Hollywood. Moore, who now runs his own company dedicated to creating apps for cell phones, notched two top-selling paid apps earlier this year: White Noise, which offers ambient, natural-environment sounds for those who can’t sleep, and Card Counter, a tutorial for would-be blackjack cheats. (“I knew I was onto something when a bunch of the Las Vegas casinos issued a warning about iPhone applications,” Moore says almost proudly.)

As for Grunberg, he went a decidedly un-Hollywood-like route with his iPhone app. Yowza!! -- the name was coined by his best friend, Star Trek and Lost auteur J.J. Abrams -- is a mobile couponing application with which on-the-go users can access deals offered by retailers. The bar code or coupon code is displayed on the iPhone or iPod Touch screen, which is then scanned or entered into the register by the store clerk at checkout. “People are turning to these apps to help them live their lives on a daily basis; plus, we’re driving traffic back into the stores that really need it,” Grunberg says.