AWS: SMS text message-based MFA

 Using multi-factor authentication (MFA) in AWS - AWS Identity and Access Management (amazon.com)

SMS text message-based MFA. A type of MFA in which the IAM user settings include the phone number of the user's SMS-compatible mobile device. When the user signs in, AWS sends a six-digit numeric code by SMS text message to the user's mobile device. The user is required to type that code on a second webpage during sign-in. Note that SMS-based MFA is available only for IAM users. You cannot use this type of MFA with the AWS account root user. For more information about enabling SMS text messaging-based MFA, see PREVIEW – Enabling SMS text message MFA devices.

Note

AWS will soon end support for SMS multi-factor authentication (MFA). We are not allowing new customers to preview this feature. We recommend that existing customers switch to one of the following alternative methods of MFA: virtual (software-based) MFA device, U2F security key, or hardware MFA device. You can view users in your account with an assigned SMS MFA device. To do so, go to the IAM console, choose Users from the navigation pane, and look for users with SMS in the MFA column of the table.