One of the more interesting features provided by the SDK is the ability for your application to use custom URL schemes to launch other applications, and in turn, to register custom URL schemes of its own. These schemes can be used to launch your application, either from the browser or from another application on the device. Additionally, such schemes are not just limited to launching the application; you can pass additional information to your application via the URL.
Most of the built-in applications Apple provides respond to custom URL schemes; for example, the Maps, Mail, YouTube, iTunes, and App Store applications will all open in response to custom URLs. However, there are also many established third-party applications with published URL schemes that you can use in your own application.
At the time of this writing, a fairly extensive list of URL schemes for third-party iPhone applications was available at http://handleopenurl.com/scheme.
You can easily trigger a telephone call from your application
by using the