2 ways -
First - make a backup copy of your sheet

If you want to leave it as it is but DISPLAY it differently, use
Format-Cells-Number, choose Custom from the left panel and under Type: enter
this code

000-0-0000-0000-0

If you actually need to change the value, in a column near the list (let's
assume the list is in column A) enter this formula along side of each entry

=text(A1,"000-0-0000-0000-0")

Copy the range of cells with the formulas, then select your original values
and use Edit-Paste Special - Values to replace the original data with the new
data, then clear all you formulas


"ian78" wrote:

I have a column 0f 3500 of numbers to convert