You can get permission for email and sms by opt-in process, This opt-in is the act of getting consent from a subscriber to send the commercial email & sms marketing messages. 

When people visit your store, this opt-in presents them with a pop-up encouraging them to subscribe for their email and mobile number. 

By entering their email address and mobile number in the box, people are giving you permission to send them email and sms as per flow setup for campaigns and automations. 

Design, content and placement of subscription popup is fully customizable to fit your preference.