[pfortuny]

There are just 10^9 phone numbers in Spain. Say 0.01 sec/hash (which is A LOT), you have 10^8 seconds. You can decrypt all the hashes in 0.3 years...

"Cryptographic hash" is as bullshit as "MD5 encrypted passwords".

[daemin]

Or you know just create a rainbow table of all the phone numbers in the world and match the hashes against that. Would probably be faster.

[Rygian]

If I'm being optimistic, the hashes of a user's contacts are salted with the user's own phone number, so the space could be 10^18.