Currently Being ModeratedFeb 3, 2013 10:24 AM (in response to PapasM)
Check out the requirements listed in the App Store. If you are talking about Viper SmartStart, it should work on iPhone 4 but is "optimized" for iPhone 5, which probably means it can handle the larger display.
Requirements: Compatible with iPhone, iPod touch and iPad. Requires iOS 4.3 or later. This app is optimized for iPhone 5.