So you have a rolodex like database in your Emacs, or you have this phone number in a mail and you want to call it. It happens you have VoIP setup and you’re using Twinkle to make your calls. Maybe you’ll then find this function useful:

(defun twinkle-call-symbol-or-region ()
  "Call the phone number at point (symbol seems good enough), or in region"
   (format "twinkle --cmd 'call %s'"
	    "[^0-9+]" "" 
	    (if (use-region-p)
		(buffer-substring (region-beginning) (region-end))
	      (thing-at-point 'symbol))))))

It happens that symbol is better than word here because some phone numbers begin with +. And some contains / or . as separators, or some other variations (spaces) so as the number is easy to read for human eyes. Twinkle will not like this.