regex - Regular Expression for finding phone numbers

Possible Duplicates:
A comprehensive regex for phone number validation
grep with regex for phone number

Hello Everyone,

I am new to Stackoverflow and I have a quick question. Let's assume we are given a large number of HTML files (large as in theoretically infinite). How can I use Regular Expressions to extract the list of Phone Numbers from all those files?

Explanation/expression will be really appreciated. The Phone numbers can be any of the following formats:

• (123) 456 7899


• (123).456.7899


• (123)-456-7899


• 123-456-7899


• 123 456 7899


• 1234567899

Thanks a lot for all your help and have a good one!