Number format switch

Hi guys!

I have several phone numbers that I copy and paste from the web:
I.E:

(888) 456-7890
(333) 234-5678

I need to switch all of them to just standard numbers: They should look like this:

8884567890
3332345678

I go to "format" - "cells" - "numbers" but nothing works. I wonder if any formula can do it. It should work for ALL THE LIST, I want something else than change them one by one by hand.

Thank you!!!
Lorena