sanitizing a phone number using a regular expression

Expanding on the regular expression found in this blog post on validating phone numbers, I’ve found a regex that seems to match any U.S. phone number I can throw at it:

^[\(]?(\d{0,3})[\)]?[\s]?[\-]?(\d{3})[\s]?[\-]?(\d{4})[\s]?[a-zA-Z]*?[\.]?[\s]?(\d*)$


Explanation of this regex:
^[\(]? string begins with optional open paren
(\d{0,3}) 3 digit area code, captured
[\)]? optional close paren
[\s]? optional whitespace
[\-]? optional dash
(\d{3}) 3 digit exchange code, captured
[\s]? optional whitespace
[\-]? optional dash
(\d{4}) 4 digit phone number, captured
[\s]? optional whitespace
[a-zA-Z]*? optional word (matches 'ext','extension','x', etc.)
[\.]? optional period (matches the '.' in 'ext.')
[\s]? optional whitespace
(\d*)$ end of the string is the extension number, which can be any length