Validating US phone number with php/regex

Question

EDIT: I\'ve mixed and modified two of the answers given below to form the full function which now does what I had wanted and then some... So I figured I

Answer 1

Why not convert any series of letters to be "x". Then that way you would have all possibilities converted to be "x".

OR

Check for 3digits, 3digits, 4digits, 1orMoreDigits and disregard any other characters inbetween

Regex: ([0-9]{3}).*?([0-9]{3}).*?([0-9]{4}).+?([0-9]{1,})