To access the page, in Navigation, go to AUDIENCE, and then select SMS Contact Lists.

Creating SMS Contact Lists
You can create a new SMS contact list using the NEW LIST button on the SMS Contact Lists page. After the list is created you can add contacts to the list either by importing contacts or manually adding them. To learn more, see Creating SMS Contact Lists.
Managing SMS Contact Lists
After a list is created, it is displayed on the SMS Contact Lists page.
You can click the name of an SMS contact list to see the list dashboard. The dashboard provides a complete view of all the relevant information and statistics.

The page also provides various actions to help you manage the lists as discussed below:
Export SMS List
Use the option to export the contacts in the list. From the Actions drop-down list, select the Export SMS List option to begin the export process. Once the process is complete, you'll receive an alert in the notification panel.
Import SMS List
Use the option to import contacts into the list. From the Actions drop-down list, select the Import SMS List option. This opens the Import Contacts dialog box where you can fill in the import details and initiate the process. To learn more about importing contacts, see the "Adding Contacts Through Import" section in Creating SMS Contact Lists.
View Contacts
Use the option to see all the contacts in the list. From the Actions drop-down list, select the View Contacts option. You'll then be redirected to the [SMS Contacts] page that displays all the contacts added to the list. On this page, you can add new contacts to the list as well as edit and delete the existing contacts. To learn more about adding contacts manually, see the "Adding Contacts Manually" section in Creating SMS Contact Lists.

You can further drill down to see a 360-degree overview of each contact by clicking the contact's phone number.

Deleting an SMS Contact
In adherence with EU’s GDPR laws, you can remove a customer’s contact identity from your Marketing Cloud account upon customer request. Simply choose a contact from the list and click on Delete SMS Contact next to their number.

The contact’s SMS number will be pseudonymized and placed in the Do Not SMS List. The contact will also be unsubscribed from all subscribed SMS lists.

What do you mean by pseudonymized?
It is a process in which we remove all sensitive and personal identifiers that relate to a customer from the registry and replace them with random placeholder values. In this way, we can retain the contact’s record and adhere to all data compliance regulations. This also reduces the risk of consumer information being accessed without authorization.
To know more about pseudonymizing a customer’s contact and its underlying data protection laws, read our Right to Erasure topic.
Edit List
Use this option to edit the list. From the Actions drop-down list, select the Edit List option. This opens the Edit List dialog box where you can update the list name.
Delete SMS List Permanently
Use this option to delete the list. From the Actions drop-down list, select the Delete SMS List Permanently option.
Managing SMS Do Not Mail List
The invalid and unsubscribed contacts are managed in the SMS DNM List. You can view and manage the list on the Manage Global Suppression List page available from Settings. To learn more, see Suppression (Do Not Mail) Lists.
Note: When an SMS campaign doesn’t get delivered to a contact, it is considered to be a delivery failure. Based on the error code, we identify the occurrence to be a temporary failure or permanent failure. The contacts from permanent failures then automatically get added to the SMS DNM list.