Scanning for numerics in a comment field

On further relection, it is ok if there are 'wrong' invoice numbers in
this mix.
I have a comment field of 40 that will have some valid invoice numbers,
and maybe non-valids like a phone number.

I just want to wade through this 40 pos. field and pick up all contiguous
numerics. I won't even be concerned about the X before it, I can add this
if I want.

The purpose here is to speed up a process by aggregating these invoice
numbers.

I am seeking the most elegant and efficient way to do this.

Thanks,
Steve