In SMS channel, the response will be text based. Someone will respond with YES or ACCEPT and your inbound SMS process will need to identify that as a positive response and continue the offer flow with the appropriate flow path. Please review the user documentation on Inbound SMS which would explain this process. I believe there are also some Pega Academy courses that you might want to review.
I don't know what you mean by Interactive, but we call inbound SMS the ability to react to a message back. So if you send and SMS to a customer. The customer replies back to the SMS with test saying YES, then the message will be received as Inbound Message and you can decide if that is an accept for the original offer or not. This is described in the Inbound SMS documentation.