Hello @blissy,

Great question!

Customers can certainly respond to the SMS messages you sent them from Klaviyo. I would suggest taking a look at our Guide to SMS Conversations in Klaviyo Help Center article which goes over how responses and conversations for SMS are managed within Klaviyo. 

Essentially, when customers reply to your SMS, you’ll be able to see the response under the SMS Conversations tab within the Klaviyo interface. Here you’ll also be able to respond directly to the recipient in a two-way communication as well! Keep in mind though that SMS conversations are not available for alphanumeric sender IDs. 

I hope this helps!

David