Hello there,
Thanks for reaching us out. We provide our plugin for WooCommerce checkout. It allows verifying phone numbers of customers and send SMS notifications include status updates. Using the plugin requires verification for all checkout activities. In order to bypass this for your existing customers, you will need to update the plugin's code and check if the provided phone number is in your DB.
Regarding bulk SMS -- we do provide this service and it works separately. In general, you'll need to provide your account creds, the list of phone numbers, SMS text, and make sure you have an appropriate amount of funds in your balance.
Please let me know if you have any other questions.
Thanks!
Emil