IsValidUsPhoneNumber - Validating a US phone number

' Validate a US phone number
' Example:
'   MessageBox.Show(IsValidUsPhoneNumber("(123) 456-7890"))  ' True
'   MessageBox.Show(IsValidUsPhoneNumber("(123) 456-78901")) ' False

Function IsValidUsPhoneNumber(ByVal phnNum As String) As Boolean
    Return System.Text.RegularExpressions.Regex.IsMatch(phnNum, _
        "^((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}$")
End Function