This is my favorite new trick and it is super easy!
Why bother? A linked telephone number allows mobile users on your web site visitors to instantly initiate the call dialog on their phones.
On a computer, the linked number works with Skype or other VOIP.
Type the phone number how you want to read it. If you use a WYSIWYG editor use the "Link" button. It often looks like a chain or a globe with a chain. Using the pull down menu change the protocol to "other". In the field type tel://+14155551234
If you prefer to write html by hand, like Dave does, your code is below. The highlighted part can be written however you prefer.
<a href="tel:+15555551212">555-555-1212</a>