Adding Dashes for an Entire Column

[u.s.s_demon]

Unsure of how I would do this for an entire column, but I need to add dashes between the first four sets of numbers. For example, 4026215160 → 4026-2151-60.

Is there a way to format an entire column to do this? Or do I have to do it one by one (if this is the case it will take an entire day as there are 1,545 cells this needs to happen to)?

[schiavinatto]

Select the column and use Format Cells, with the format
####"-"####"-"##

[LeroyG]

If do you need to change the cell content (not only the display formatting), search for ^(.{4})(.{4})(.{1,}) and replace with $1-$2-$3.

This would work for numbers with 9 or more digits.