> Now, with some simple filtering and statistics, WhatsApp the service can deduce your phone book with some certainty, but I believe most would agree that it is

> Now, with some simple filtering and statistics, WhatsApp the service can deduce your phone book with some certainty, but I believe most would agree that it is materially different from actually uploading your phone book. No, not really. Both implementations give WhatsApp a complete list of all my contacts. The fact that one of those implementations might not be 100% accurate because of deleted contacts changes nothing - if you're someone who's worried about a third party having your contact list, it doesn't make sense to think "but hey, they don't know I removed $FOO last week, so their list isn't 100% accurate!". Both implementations mean you'll have to take their word on what they will and won't do with the data, so there's really not much of a practical difference.