How to mark-up phone numbers?

I want to mark up a phone number as callable link in an HTML document. I have read the microformats approach, and I know, that the tel: scheme would be standard, but is quite literally nowhere implemented.

Skype defines, as far as I know, skype: and callto:, the latter having gained some popularity. I assume, that other companies have either other schemes or jump on the callto: train.

What would be a best practice to mark-up a phone number, so that as many people as possible with VoIP software can just click on a link to get a call?

Bonus question: Does anyone know about complications with emergency numbers such as 911 in US or 110 in Germany?

Cheers,

Update: Microsoft NetMeeting takes callto: schemes under WinXP. This question suggests, that Microsoft Office Communicator will handle tel: schemes but not callto: ones. Great, Redmond!

Update 2: Two and a half years later now. It seems to boil down to what you want to do with the number. In mobile context, tel: is the way to go. Targeting desktops it's up to you, if you think your users are more Skype people (callto:) or will more likely have something like Google Voice (tel:) installed. My personal opinion is, when in doubt use tel: (in line with @Sidnicious' answer).

Update 3: User @rybo111 noted, that Skype in Chrome has meanwhile jumped on the tel: bandwagon. I cannot verify this, because no machine with both at hand, but if it's true, it means we have finally a winner here: tel:

Solution 1:

The tel: scheme was used in the late 1990s and documented in early 2000 with RFC 2806 (which was obsoleted by the more-thorough RFC 3966 in 2004) and continues to be improved. Supporting tel: on the iPhone was not an arbitrary decision.

callto:, while supported by Skype, is not a standard and should be avoided unless specifically targeting Skype users.

Me? I'd just start including properly-formed tel: URIs on your pages (without sniffing the user agent) and wait for the rest of the world's phones to catch up :) .

Example:

<a href="tel:+18475555555">1-847-555-5555</a>

Solution 2:

My test results:

callto:

Nokia Browser: nothing happens
Google Chrome: asks to run skype to call the number
Firefox: asks to choose a program to call the number
IE: asks to run skype to call the number

tel:

Nokia Browser: working
Google Chrome: nothing happens
Firefox: "Firefox doesnt know how to open this url"
IE: could not find url

Solution 3:

The best bet is to start off with tel: which works on all mobiles

Then put in this code, which will only run when on a desktop, and only when a link is clicked.

I'm using http://detectmobilebrowsers.com/ to detect mobile browsers, you can use whatever method you prefer

if (!jQuery.browser.mobile) {
    jQuery('body').on('click', 'a[href^="tel:"]', function() {
            jQuery(this).attr('href', 
                jQuery(this).attr('href').replace(/^tel:/, 'callto:'));
    });
}

So basically you cover all your bases.

tel: works on all phones to open the dialer with the number

callto: works on your computer to connect to skype from firefox, chrome

Solution 4:

As one would expect, WebKit's support of tel: extends to the Android mobile browser as well - FYI

Solution 5:

I keep this answer for "historic" purpose but don't recommend it anymore. See @Sidnicious' answer above and my Update 2.

Since it looks like a draw between callto and tel guys, I want to throw in a possible solution in the hope, that your comments will bring me back on the way of light ;-)

Using callto:, since most desktop clients will handle it:

<a href="callto:0123456789">call me</a>

Then, if the client is an iPhone, replace the links:

window.onload = function () {
  if (navigator.userAgent.match (/iPhone/i)) {
    var a = document.getElementsByTagName ("a");
    for (var i = 0; i < a.length; i++) {
      if (a[i].getAttribute ('href').search (/callto:/i) === 0) {
        a[i].setAttribute ('href', a[i].getAttribute ('href').replace (/^callto:/, "tel:"));
      }
    }
  }
};

Any objections against this solution? Should I preferably start from tel:?