How to create hyperlink to call phone number on mobile devices?

Question

What is the proper, universal format for creating a clickable hyperlink for users on mobile devices to call a phone number?

Area code with dashes

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Answer 1

I used:

Tel: +123 123456789

and the result is:

Tel: +123 123456789

Where "Tel:" stands for pure text and only the number is coded and clickable.