If you type that number in, then type it as '09123456789, i.e. with a

leading apostrophe. The apostrophe will not show in the cell.

If you have a lot of these values, say in column A, then you could use

column B with a formula like this:

=TEXT(A1,"00000000000")

if your values are all 11 digits long, and copy this down. You could

then fix the values in column B, and delete column A.

Hope this helps.

Pete