These are URL schemes supported by native apps on iOS, OS X, and watchOS 2 and later.

Opening link in Safari:

Objective-C

NSString *stringURL = @"<http://stackoverflow.com/>";
NSURL *url = [NSURL URLWithString:stringURL];
[[UIApplication sharedApplication] openURL:url];

Swift:

let stringURL = "<http://stackoverflow.com/>"
if let url = URL(string: stringURL) {
    UIApplication.shared.openURL(url)
}

Starting a phone conversation

Objective-C

NSString *stringURL = @"tel:1-408-555-5555";
NSURL *url = [NSURL URLWithString:stringURL];
[[UIApplication sharedApplication] openURL:url];

Swift:

let stringURL = "tel:1-408-555-5555"
if let url = URL(string: stringURL) {
    UIApplication.shared.openURL(url)
}

HTML

<a href="tel:1-408-555-5555">1-408-555-5555</a>

Starting a FaceTime conversation

Objective-C

NSString *stringURL = @"facetime:14085551234";
NSURL *url = [NSURL URLWithString:stringURL];
[[UIApplication sharedApplication] openURL:url];

Swift:

let stringURL = "facetime:14085551234"
if let url = URL(string: stringURL) {
    UIApplication.shared.openURL(url)
}

HTML

<a href="facetime:14085551234">Connect using FaceTime</a>
<a href="facetime:[email protected]">Connect using FaceTime</a>