Opposite of concatenate / adding in extra info to a large number

I have cells with a string of numeric characters in it (i.e. 12345678) and I want to split it, in one cell, to read as 123.456.78
Can anybody please tell me if this is possible?
Thanks!

If your original number is in A1, enter the following into the cell you want the amended version in:

=LEFT(A1,3)&"."&MID(A1,4,3)&"."&RIGHT(A1,2)

I'm sure there are prettier ways of managing this, but it does the job for now.

EDIT: I think Haru is reading my mind!!!!

Thanks people, much appreciated!