How do you write a phone number that triggers a call?
Choose the telephone record type and enter the number in full international format. Tapping the tag opens the dialler with the number ready, and the user still has to press call. No platform places a call from a tag without confirmation, and that is deliberate.
It prefills, it does not dial
Expectations here are usually wrong, and correcting them early saves a support conversation.
Tapping a telephone tag opens the dialler with the number entered. The person still presses the call button. Neither platform will place a call because an object was touched, which is obviously the right decision: a tag on a wall that could ring a premium number by proximity would be a fine piece of fraud.
Write the number properly
Full international format, with the country code, and no spaces, brackets or dashes. A number written for local dialling works at home and fails for anyone from elsewhere, which defeats the purpose on anything a stranger might tap.
The telephone scheme is one of the prefixes the URI record abbreviates to a single byte, so a phone number tag is small and fits on anything.
Where this is genuinely useful
Places where someone needs to reach a specific number quickly and does not know it: a helpdesk sticker on a machine, a contact point beside a locked door, a taxi number in a hotel room, a support number on equipment in the field.
What these share is urgency and unfamiliarity. Tapping is faster than reading a number and typing it, and it removes transcription errors, which is a real benefit when someone is stressed.
When a number is the wrong answer
When the destination might change. A tag holding a number is as frozen as one holding a vCard, and a support line that moves leaves a wall of tags pointing at nothing.
When you would rather they did not call. Many support tags exist because nobody wanted a phone call at all, and a URL to a page with a form, a chat option and the number as a last resort serves everyone better.
And when you want to know the tag was used. A phone call tells you nothing about which tag was tapped, while a link through your own domain does.
Frequently asked questions
Can a tag place a call automatically?
No, on either platform. The dialler is prefilled and the user confirms, which prevents a tag from initiating a chargeable action without consent.
Should I include the country code?
Always, for anything a visitor from elsewhere might tap. A locally formatted number is a tag that works for people who already knew the number and fails for everyone else.
Can I add an extension to the number?
The telephone scheme supports pause and wait characters for extensions, and support for them varies by dialler. Test on the target devices rather than assuming, since a failed extension is worse than none.
Does a phone number tag work offline?
Yes. The number is on the tag and the dialler is local, so it works with no coverage at all. This is one of the arguments for it over a link.