Time for another geek interlude – tel: versus callto:
Taking WAP out of the equation because it’s so old as to be irrelevant, there are two ways to mark up telephone numbers in HTML. The tel: URI (Universal Resource Indicator – it tells your browser what it can expect to find at the destination of your link) is the official standard for marking up telephone numbers whilst callto: is a proprietary URI made popular by Skype and unsurprisingly, Microsoft.
By marking up a telephone number, it makes it easier for visitors to your website to make phone calls from their phones or computers – click on the link and it launches whichever application is set up to handle phone calls. But the problem is, which of the two do you accommodate on your website? Mobile devices are the obvious target because they’re usually going to be mobile phones so tel: would seem to be the obvious choice but it’s not uncommon for people to have Skype phones or another VoIP phone service so callto: support would be useful.
But you can’t have both so which should you use? Do you encourage standards compliance by using tel: or pander to the embrace and extend ethos of Sky and Microsoft and use callto:? Do you cater for mobile devices with tel: or desktops with callto:?
With the rapid convergence of internet and phones, we need some standards compliance in the major browsers. The last thing we need is a VHS/Betamax or Blueray/HD-DVD battle over telephone number markup standards!