Everyone keeps talking about Smule's virtual lighter iPhone application called Sonic Lighter ( iTunes link ). I wasn't impressed: there are no less than ten different virtual lighter apps in iTunes, which is what I'd call a saturated market. And it gets better, because Sonic Lighter costs $.99. The official Zippo iphone app is free. The basic functionality of all of these is similar - you have a virtual lighter, you light it and when you move the iPhone the flame moves around. The number of downloads for Zippo isn't available; Sonic Lighter says they've had 70,000 downloads already. But here's one way to compare them: that the free Zippo app has been available since September 18 and has just 27 reviews. Sonic Lighter, which has only been available since Wednesday, already has 44. Here's why people are going crazy for Sonic Lighter, and are willing to pay $.99. Smule has built in social and viral features that are helping this spread like mad, and they also give this ridiculous but effective incentive to use the app all the time.