zlacker

A Flow:

> Service A => User: Please Enter Your Phone Number and Email

> Service A => Clearinghouse: Please verify phone number XXX wants to sign up for an account with us

> Clearinghouse => User (SMS): Please respond with the Email you used at signup to confirm you want an account with Service A

Later...

> Service B => User: Please Enter Your phone number and Email

> Service B => Clearinghouse: Please verify phone number XXX wants to sign up for an account with us

> Clearinghouse => User (Email): Please verify you want an account with Service B

Not saying it's great (providing email twice is annoying), but it's something.

>>explai+(OP)
This does not reduce the overall cost, it just shifts it to the clearinghouse. Who pays the clearinghouse so that they can cover their own exorbitant SMS costs?

>>rezona+v3
You miss the crux of it: the second time onward the clearing houses uses email to authenticate the previously-SMS-verified account.

>>explai+H9
The clearinghouse may not have the user’s most recent email address, which is common amongst non-tech people. My mom and aunts have lost many email addresses this way and forcing them to use an older email would cause many issues.

>>supriy+Na
The app has to ask for email/phone to begin with (see step 1), if the email doesn't match then phone would be used as fallback, or potentially as a "Didn't Receive Code?" gesture.