How many consumers think about buying an application or mobile game in an app store but then change their mind and don't install it? It's a pretty difficult figure to know. However, there are a growing number of firms that are focused on increasing the exposure developers can provide to potential customers through mobile ads. These startups say offering a test drive of sorts will not only increase the likelihood of converting tire kickers into active users, but that those users are more likely to be highly engaged. Last month, for example, Voxel launched its service, which allows consumers to try out a version of the game that's available directly in an ad. Apple (NASDAQ: AAPL) is even getting into the "app preview" game a little bit and said Tuesday it will allow developers to create short videos of their apps highlighting features that can be viewed by App Store shoppers. For more on this trend, check out this FierceDeveloper special report.