Adding a dash to phone numbers

[Jim]

Hello,

I have a column of phone numbers with seven digits. I need to add a dash
after the third digit - what is hte best way to do this?

Thanks

 

[Sheeloo]

Choose
Edit ->Format Cells->Number->Special->Phone Number

 

[Jeff]

Jim - For a phone number in cell A1, type in B1:
=left(a1,3)&"-"&right(A1,4)