Well there are 10^9 or 1000000000 different ones. Thats only 1 billion. There are in fact less because of the restrictive numbering scheme (first three numbers indicate the “area” you applied for the number) I think a new, more secure system will be designed before we hit that number, or as mowens said we will just recycle old ones.
I don’t think so because
A: People die and perhaps those numbers get “recycled” and
B: Even if we got all the way to 999–99-9999 then we would just add a tenth digit.