Do you want to do with VBA or a worksheet function in another column?
What does your macro do with the account numbers? Post the code.
With a worksheet function :-
<TABLE style="WIDTH: 246pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=328 border=0 x:str><COLGROUP><COL style="WIDTH: 246pt; mso-width-source: userset; mso-width-alt: 11995" width=328><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 246pt; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=328 height=17 x:str="'=LEFT(A1,3) & "-" & MID(A1,4,4) & "-" & RIGHT(A1,4)">=LEFT(A1,3) & "-" & MID(A1,4,4) & "-" & RIGHT(A1,4)</TD></TR></TBODY></TABLE>