grep with regex for phone number

Question

I would like to get the phone numbers from a file. I know the numbers have different forms, I can handle for a single one, but don\'t know how to get a uniform regex. For ex

Answer 1

grep '\(([0-9]\{3\})\|[0-9]\{3\}\)[ -]\?[0-9]\{3\}[ -]\?[0-9]\{4\}' file

Explanation:

([0-9]\{3\}) three digits inside parentheses

\| or

[0-9]\{3\} three digits not inside parens

...with grouping parentheses - \(...\) - around the alternation so the rest of the regex behaves the same no matter which alternative matches.