[moab]

Why on earth would you have to brute force all numbers? You can do this optimally: just hash the numbers you see (or get requests for).

[dmurray]

So that I can cold call someone who might be interested in my product, even though DataLogix only told me the hash of their phone number.

[moab]

You've already hashed all numbers on your end, so it's trivial to figure this out (hash the hash?). Hopefully I'm not thinking about this wrong, but it does seem feasible.