The phone number hash used in Kontalk JIDs are SHA-1 hashes generated from E.164 phone numbers.
Example phone number:
+1 (555) 521-5554
The phone number to hash will be:
+15555215554
The resulting hash will be:
4bdd4f929f3a1062253e4e496bafba0bdfb5db75
A JID for this number would be: