In addition to the set of personalization strings available for MobileConnect, Marketing Cloud also includes AMPscript functions for using SMS conversations in MobileConnect.
SMS conversations enable message chains to be created. In a conversation, MobileConnect prefixes a Next Keyword to the Contact’s response. In turn, a keyword prefix is not required when a Contact sends a Mobile Originated (MO) message and their response can trigger the sending of another SMS message to the Contact.
NOTE: By default, a conversation remains open for 60 minutes after you send an outbound message or receive a message from a Contact. However this can be changed by opening a support case with your Marketing Cloud Support Representative.