A tel: URI turns a phone number into something a device can dial. On a phone it opens the dialler with the number filled in; on a desktop it hands off to whatever calling application is registered, or does nothing at all.
The scheme.
| Defined by | RFC 3966 |
|---|---|
| Global format | tel:+919876543210 — the leading + is required |
| Local format | tel:9876543210;phone-context=+91 |
| Visual separators | Hyphens and dots are permitted and ignored by the dialler |
| Extensions | Appended as ;ext=1234 |
| Pause before extension | A comma in the digits, honoured by most diallers |
Use the global form with the plus sign on any public page. A local number without context is only dialable from inside the same country, and a page on the open web has no idea where it is being read.
Where this shows up.
The call button on a contact card is a tel: link and nothing more. Getting the format right is the difference between one tap and a visitor copying digits by hand — which is where most contact pages quietly lose the call.
The common mistake.
Writing the number the way it is printed on a signboard, with spaces and brackets, and omitting the country code. It dials for people at home and fails for everyone travelling, which is exactly the audience a digital card is for.
Sources.
Every figure above is from one of these. They are the standard, the registry or the platform’s own documentation — read them rather than take our word for it.