I use this to format US phone numbers as 10 straight digits. Once you do this, you can use substr to split it up and insert parens or dots or hyphens or what have you...

sub format_phone {
  my @out = @_;
  foreach (@out){
    tr/a-cA-C/2/; tr/d-fD-F/3/; # change letters to digits.
    tr/g-iG-I/4/; tr/j-lJ-L/5/;
    tr/m-oM-O/6/; tr/p-sP-S/7/;
    tr/t-vT-V/8/; tr/w-zW-Z/9/;
    s/[^\d]//g;                 # remove non-digits.
    s/^1//g;                    # remove first digit if it's a one.
    $_ = pack( 'A10', $_ );     # Only take the first ten digits.
  }
  return wantarray ? @out : $out[0];
}
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Since there seems to be no standard place for the 'Q' or the 'Z' on the numeric keypad, I put them where I like them; sequentially. I've seen some phones that put them both on the nine or the zero, for some reason passing understanding. If you want them somewhere else, I won't complain.