Maybe just using format|cells|Number tab|custom would be enough.

Give it a format of:
000-0-0000-0000-0

This changes the display--not the value.

If you need to change the value, you could use a helper column of cells:
=text(a1,"000-0-0000-0000-0")
copy down the column
and edit|copy, edit|paste special|values over the original range. Then delete
the helper column.

ps. It's better to write your question in the body of the message--not just the
subject line.

ian78 wrote:

I have a column 0f 3500 of numbers to convert

--

Dave Peterson