Keychain remote start / door unlock devices have been around for years.  And, with all keychain devices, you had to be within a certain range for the device to work.  The Viper SmartStart App for iPhone features: lock /arm, unlock / disarm, remote start, trunk release, and panic / car finder.  It will work anywhere your iPhone and car are receiving a cellular signal.  The app is free but the hardware will cost $500 for a complete installation or $300 as an upgrade to your existing viper hardware.