You can try this plugin https://elgg.org/plugins/553265

WordPress is ahead of us on this topic: Two-Factor Authentication for WordPress. https://github.com/georgestephanis/tw…

There are numerous providers that do SMS out, and many of those do SMS in at an extra cost via a web or email gateway.

Some are providers better than others, some are limited to specific countries. Most charge per SMS out, and a monthly rental for SMS in.

The ability for Elgg to receive SMS is the meaner trick.

SMS delivery can be inconsistent even with reputable suppliers as regulations and quality of infrastructure vary from region to region.

According to Lucy Zhao, Product Marketing @Plivo (Global SMS API), The verification process that you're referring to is two-factor authentication. Some companies take the time and money to build their own telecom infrastructure to achieve this and other like Whatsapp use a SMS API service like Plivo, for two-factor authentication.

Here are the steps:

You download Whatsapp and it prompts you to enter your mobile #
You input your mobile phone number and choose whether you want Whatsapp to call or text you the verification code.
This triggers Whatsapp to send a randomized code in a pre-written template from one of their procured SMS-enabled numbers (i.e., long code or short code) to your mobile phone.
In the case of a phone call, Whatsapp puts together the same message, except it calls your mobile and gets a text to speech engine to read the message.
When Whatsapp receives your input, it matches the code you registered with.

Here's a sample two-factor app that works with Plivo:
https://github.com/sandeepraju/e...

You can also read more about how mobile apps are using Plivo for two-factor authentication: https://www.plivo.com/customers/...
 

For more info you can read: https://www.quora.com/How-can-I-implement-sms-verification-like-WhatsApp-in-my-iPhone-application

Learn how to verify phone numbers on: iPhone | Windows Phone | Nokia S40 | BlackBerry | Nokia S60 | BlackBerry 10

For further reading you can read here  https://www.ibm.com/developerworks/web/library/mo-sms-web/index.html?cmp=dw&cpb=dwwdv&ct=dwnew&cr=dwnen&ccy=zz&csr=111011

What’s Wrong With SMS Authentication? Two IBM Experts Weigh In on the NIST Recommendation

https://securityintelligence.com/whats-wrong-with-sms-authentication-two-ibm-experts-weigh-in-on-the-nist-recommendation/

Thank you Tom, very helpful.

Once upon a time I have built Twilio integration for ArckInteractive. https://github.com/arckinteractive/elgg-twilio-sms

You would still have to build your auth module, but it provides the foundation to actually deliver SMS via Twilio.