The first big native application that I remember using was Facebook. The mobile Facebook application was awesome and allowed you to do almost everything that the website did, but with an interface specially designed for interaction on a hand-held device. Indeed, as popular as Facebook at the time already was, putting a tool that powerful in the hands of iPhone owners all over the world helped Facebook, quite literally, change the world.
For some applications, it may be necessary to write a custom native application for the handhelds to interact with your Drupal website. Android Market and the Apple AppStore have made billions for their respective companies by creating an ecosystem of native hand-held applications. For this application to interact with an Internet-based backend, it's usually better to pick a single method of communication and use that method throughout your application so that you can write a single interface to call and interpret...