What about this?

sub andify {
  return '' unless @_;
  return $_[0] if @_ == 1;
  local $" = @_ == 2 ? ' ' : ', ';
  $_[-1] = 'and ' . $_[-1];
  return "@_";
}
[download]

Fixed squiggly brackets and should be $" not $,.
Fixed comma placement.
Got rid of blackberry comment.
Handled null case.
Changed regex to concatenation

20050525 Edit by ysth: p, code tags