send sms to mobile number for authentication.

Appian has no default feature around it. You can do it via an email by generating a random 4-6 digit code and then sending it via an email but not SMS.
You can use any of the SMS-sending APIs for it. Just google and you'll have a lot of such service providers. 

you can try this:

community.appian.com/.../nexmo-connected-system

Yes, you can send an SMS to a mobile number for authentication purposes. Here's a general idea of how you can do it:

1. The user provides their mobile number on your form or application.
2. Your application generates an OTP (One-Time Password) and sends it to the user's mobile number via an SMS API.
3. The user enters the OTP they received on their mobile device into your form or application.
4. Your application verifies the OTP to ensure it's correct.
5. If the OTP is verified, the user is granted access to the desired resource, or the form is submitted.

To send SMS messages, you will need to use an SMS API such as Twilio, Nexmo, or others. These APIs provide a way to send SMS messages programmatically, allowing you to automate the process of sending OTPs for authentication.

This is a common method for adding an extra layer of security to authentication processes, as the OTP is only valid for a short period of time and is sent to a device that the user has access to, adding an extra level of assurance that the person attempting to access the resource is indeed the intended user.

Source: Bulk SMS Service Provider