> Invite codes worked fine for Gmail
Back in 2004, sure. Today, Gmail asks you for a phone number when signing up because of the spam problem.
Back in 2004, sure. Today, Gmail asks you for a phone number when signing up because of the spam problem.
If you're saying that the account creation flow through the system accounts application doesn't require a phone number, how are you sure that Google doesn't just collect the phone number directly from your device (they could even silently verify it through a class-0 silent SMS)?
Does it also not ask for a phone number if you factory reset, remove the SIM card, and do not register the phone with a Google account? Maybe they track the IMEI instead?
In the case of Twitter, there is evidence that the initial implementation was meant to just be a security mechanism but later someone else noticed they had a handy database of user phone numbers and decided to treat them as free marketing contact information.