You may want a double opt-in process for SMS contacts that you are adding to your account. Generally speaking this is done by adding contacts as a specific contact status, needs-confirm. While this is supported if you are manually importing a CSV file, the API does not support the ability to add SMS contacts as any status other than normal.
If you need to add SMS contacts manually and send a confirmation message, please visit this article for how-to steps that can be performed inside your account.
Article is closed for comments.