https://codecanyon.net/item/digits-wordpress-mobile-number-signup-and-login/19801105

Digits let your user signup on your website simply with their mobile number. No more checking emails. Just SMS In this fast world, no one has time to SignUp on your website using traditional email, because this is not the single step involved, user has to log into the email account – open email – click on the verification link to verify the email and then he/she gets access to the account on your website.