Apple Phone Links


"The tel URL scheme is used to launch the Phone application and initiate dialing of the specified phone number. Tapping a telephone link on a webpage displays an alert asking if the user really wants to dial the phone number and initiates dialing if the user accepts. In a native application, opening a URL with the tel scheme initiates dialing without further prompting from the user" (source: Apple Developer website)

Application homepage:
iTunes link:
HTML Link example: <a href="tel:0031204637000">Call us</a>
Native application URL string example: tel:0031204637000
Extended example:

More information can be found at the Apple Developer website