What&#x27;s probably slowed adoption of that approach is too much &quot;web thinking&quot; in the app design process and too much &quot;But what does Google &#x2F; Facebook &#x2F; Twitter do?&quot;<p>In fact Twitter provides SMS based signup as a free service for app developers as part of Fabric - <a href="https:&#x2F;&#x2F;get.digits.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;get.digits.com&#x2F;</a>